Page images
PDF
EPUB

THE

globe, the operations of reading and writing occur in our own land. Such, however, has can be carried on with perfect facility at an been the case. The great earth wave has made elevation which reaches above the clouds. its vibrations felt at our own doors, and the So long as the clouds are held in suspension puny, although highly effective, representaMECHANICS' MAGAZINE. by an upward current of air, they are either tions of man at the Polytechnic Institution

LONDON: FRIDAY, NOVEMBER 6, 1868.

UP IN A BALLOON.

The motion of

immovable, or they rise; when the current possess a real meaning to our west of Engfails, they fall. M. Flammarion gives a vivid | Îand friends. The recent shock was very account of the formation of the clouds over distinctly felt about twenty minutes before the valley of the Rhine, viewed from an alti-eleven o'clock last Friday night, and it extude of 7,000ft. above the historical town of tended over a considerable area in the west IN anyone quarter to four a.m. At half-past four, clouds about a couple of secondi, and in som sitter N a very short space of time, anyone who Aix-la-Chapelle. The sun rose at about a of England and South Wales. It lasted for regarded as a man behind the age, and will commenced to form underneath the observers, tions was said to have been very severe, be ranked in the same category as one who at a distance nearly half way between them whilst in others it is described as being but has never been in a "Hansom " or on a rail- and the earth. Shortly afterwards, the earth, slight. The night on which the shock occurred way. It is, in short, the proper thing to do, which had been distinctly visible hitherto, was cloudy but light, the moon being nearly and it will altogether depend upon the probecame hidden from view by immense fleecy at the full. Taking the various accounts that clivities of the aeorostat whether he makes masses, which congregated at one point and have appeared from observers of the phenohis atmospheric voyage with scientific or dispersed at another with astonishing rapidity. menon, we find its indications variously demerely commonplace intentions. If with the With the rising of the sun, and the consequent scribed. Some describe it as a trembling of latter solely, he will be amply repaid by the increase of temperature, the balloon mounted, the earth, as a laden waggon was passing panorama spread out beneath his view. The and the clouds likewise, until the latter along the street; others imagined some anicoup d'œil will be beyond his most sanguine arranged themselves immediately underneath mal had got in their bedroom and was scamexpectations, and he will return to terra firma the former, and, after remaining a short time, pering about the floor. at least a wiser man than when he quitted it. disappeared with the same celerity with which articles of furniture, the jingling of glasses, Our intention in the present article is not to they were created. and the oscillation of beds, were very comdilate upon the interesting features that may Leaving what we may call the lower mon. Most of the reports agree that these present themselves to the eye of the amateur, regions, namely, those of the cumulo-stratus, indications were accompanied by a noise like but to record some of the phenomena that and soaring into the space beyond, the that of a high wind, or of a vehicle or train attract the attention of the savan, the chemist, "cirrus" appear to be as far above the passing. Reports from towns and villages and the philosopher. Meteorologists have observer as if he had not left the terrestial westward of Worcester describe the shock reduced the various conditions and appearsurface. One seems to be, as it were, in very similar terms. In Leamington, three ances afforded by the clouds and the regions between two skies, one above and the other shocks followed each other in rapid succesof air into nine distinct subdivisions. M. below. At an elevation of 13,000ft., the supe- sion. The shocks were noticed by Dr. Flammarion, in an exceedingly interesting rior vault loses its concave appearance, and O'Callaghan, LL.D., the president of the paper read before L'Academie des Sciences, the inferior appears to solidify. With a clear local philosophical society, who, during a has further reduced these subdivisions to two. atmosphere, the earth, instead of presenting residence in the West Indies, had on more He designates the clouds that appear nearest a convex form, has, on the contrary, a con- than one occasion felt the shock of earththe earth, or what we terrestrials would call cave surface. That the clouds are due to the quakes. On Friday night, Dr. O'Callaghan the clouds proper, by the name of cumulo- condensation of the humidity existing in the called attention to the occurrence, and found air, is the result of all the meteorological ob- that the shocks had been observed by some servations made with the view of ascertain- of his domestics. At Exeter, many persons noticed the earthquake. Three distinct shocks were felt by the inmates of a house in York-buildings. The occupant of a house, who has long resided in the West Indies, recognized the shaking as that of an earthquake. The inmates of the Eye Infirmary felt the building shake, and experienced a peculiar sensation at the time.

stratus. These viewed from a balloon semble large masses

re

of grey vapour, or gigantic bales of cotton. Under the second classification of cirrus, he includes the small light fleecy-looking clouds that are pendent high up in the blue vault of the firmament, slightly tinged towards the evening, sometimes of a dappled appearance, and at others streaked with a rosy irridescence. We omit all consideration of the "stratus," which are visible only in the daytime, and the "nimbus," which are the forerunners of the

dissolution of snow into rain.

may

?

At

Reports from Merthyr state the shock to have been rather severe, the movement appearing to be from south to north and continuing for three or four seconds. A few minutes before the occurrence there was that strange calm prevalent which has been noticed during the time of a complete eclipse. Great alarm was felt by the inhabitants. Twynrodyn and other high quarters, the in some coal or mine pits; but as Merthyr people rushed out of the houses, some attributing the shock to explosions underneath tum exists there, this fact was conclusive that is not undermined, and no mine or coal strathe disturbance proceeded from a greater and mysterious cause. We will conclude with a report from a meteorologist of some years standing, who writes from Port Talbot, South Wales. He says:-"The night was wet, with a drizzling rain, and a strong S. W. wind blowSoon after ing. Barometer stood at 29.50. 10 p.m. the wind abated; then followed a lull, with an overcast sky. At 10-35 p.m., as I was sitting with a friend in my drawingperienced a dead, heavy thump, as if from room, on the ground floor, suddenly we exside the window, followed, after the interval the fall of a bale of goods close out

ing the nature and origin of their formation. Currents ascending from a humid region, and traversing a certain zone or belt, have their humidity condensed and rendered visible, which was previously invisible. A very curious phenomenon has been observed from the elevated position of a balloon, and recorded by M. Flammarion. During one of his aerial voyages his attention was attracted to a cloud, about 600ft. in length by 450ft. in breadth, which remained in a state of imConfining ourselves, therefore, to the two de- movable suspension at an elevation of nearly scriptions of aeriform phenomena that we have 300ft. above some trees. The other clouds mentioned, it has been determined that the in the meantime were passing at the rate of first, the cumulo-stratus or clouds proper, are 25ft. per second. What invisible anchor held situated at an average distance from the this particular mass of vapour from particiearth of 4,000ft. They are occasionally met pating in the motion of its neighbours with both above and below this distance. Upon steering the ballcon below the object found nearer to the earth than 20,000ft. It cloud was stationary immediately above a The cirrus or superior clouds are rarely to be of observation, it was discovered that the has long been a problem to the philosopher clouds, also immovable, traced out in space large piece of water, and that some smaller to ascertain what thickness of cloud was the course of a stream. No explanation has necessary to obstruct the rays of the sun. been offered of this curious fact, but it is During a voyage in a balloon, recently made, attraction may exist the sun was obscured for some time after possible that some between the clouds and the sources from commencing the ascent, but after continuing to rise until the belt of clouds was left below, which they are created. The physical contheir thickness was ascertained to be about tours of a country are readily distinguished 620ft. The light of the sun was therefore by the experienced aeronaut. He can tell at unable to traverse this mass of cloudy opacity. tints they present to the rising sun. a glance the plains and the valleys by the The The degree of humidity registered by the hygrometer was a maximum at the lower surplains are dark and shadowy, while the face of the mass of clouds, and a minimum at the valleys whiten and glisten beneath its beams. upper, the range being rather more than 5deg. and the thermometer invariably registers a This is caused by the condensation of vapour, At the same time, the temperature obeyed a very lower degree for the valleys than the plains. different law. Marking 20deg. at the ground With increased facilities for observing the of a second, by a tremulous motion through level, the thermometer descended to 15deg. condition of the upper regions at various the room, which shook the floor beneath our at an elevation of 1,900ft. Entering into the times and seasons, it is only to be expected regions of clouds, it rose to 19deg., and con- that a large augmentation will be made to feet, and rattled some ornaments on a side tinued to rise as the elevation increased. The aerial our present knowledge of meteorology, the table, the shock passing from N.W. to S.E., when emerging from the voyageur, misty, gloomy, and melancholy æther of the hygrometric state of the atmosphere, and and occupying about five or six seconds of cloudy belt into the upper regions, experi- ultimately of the key of all science, astro-time. The effect upon me and my friend was ences a joyful and exhilarating sensation nomy. which is perhaps enhanced by observing that the earth which he has quitted appears to be metaphorical allusion, for when the veil of darkness has descended upon the terrestrial

AN EARTHQUAKE IN ENGLAND.

but

Nather frequent off Nature have been
rather frequent of late in foreign parts,
one suspected they would ever

no

unmistakable. We at once exclaimed, An earthquake! My house stands alone on a hill, with gardeners' cottages near. My servants, who were in their bedrooms, ran out

to know what was the matter, and those down stairs were equally at a loss to know the cause of the noise. My gardeners and their

families were similarly surprised, but felt it could be no other than an earthquake. I find that people who were out of doors at the time did not feel the shock."

DOUBLE AND SINGLE-HEADED

RAILS.

Tquestionably the simplest to lay, since
THE contractors' or Vignoles rail is un-

be said with much success. The incessant about a minute, or with three men may be
jar and vibration that a permanent way is opened in less time. We are informed that
subject to appears to set at defiance all means one man has actually opened the bridge in
hitherto applied for practically overcoming two minutes. The contract for the general
the inconveniences it gives rise to.
ironwork of the bridge was taken by Messrs.
The double-headed rails are more readily Finch and Heath, Chepstow, who were the
removed and replaced than the Vignoles, for builders of Brunel's celebrated bridge at
as they are not directly fastened to the Chepstow, and appears to be well carried out.
sleepers, all that is necessary is to knock The hand railing is being executed by Messrs.
out of their chairs, stilarly, new sleepers
away the keys and fastenings and lift them Harris and Son, of Marsh-street, Bristol.

THE CIVIL AND MECHANICAL
ENGINEERS' SOCIETY.

ΟΝ

it requires no chairs or keys of any kind. It are readily substituted for the worn-out ones, is, therefore, not surprising that many com- as sleepers and chairs can be removed panies give it the preference in their perma- together, while another, with its chairs fixed nent way, particularly when the road is laid on, can be slipped in at once. M. Séverac upon transverse sleepers. At the same time, states, in support of his prediliction for the the double-headed rail has its advantages and double-headed rail, that its manufacture does N Saturday last, the first annual dinner its supporters also. The objections alleged not present so many difficulties as the flanged Anderton's Hotel, Fleet-street, a goodly numof the above Society took place at against the latter are that, in the first place, example, and that therefore it can be obtained ber of members and visitors attending. it necessitates the expense of chairs; and cheaper in the iron market. We have doubts Amongst those present were the following:that, secondly, the turning of them, in which respecting this assumption, and are inclined Members of Council-Mr. B. Haughton, Pretheir chief merit lies, cannot be accomplished to believe that the price per ton would not sident; Mr. W. F. Black, Vice-President; universally. If every rail could always be vary to any extent worth consideration. Messrs. F. Cooper, W. Meakin, R. M. Banturned, so as really to do the duty of two, There is, however, truth in the observation croft, G. W. Usill, G. W. Willcocks, F. H. then the increased amount of work got out of that the double-headed rail is better adapted Roberts (hon. sec.), and G. J. Dawson (hon. the rail would more than compensate for the for sharp curves, owing to the greater facility treasurer). Amongst the members present expense of the chairs, and, cæteris paribus, it possesses for being bent to the required it would prove more economical than the radius. The flange of the Vignoles rail, by T. Kell, A. H. Lavers, H. G. Powell, G. H. were Messrs. G. E. Eachus, G. R. Godson, flanged description. To effect this result, its comparative large breadth, bends with Royce, R. T. White, J. B. Walton, &c.; and two precautionary measures must be under- difficulty, and incurs a greater chance of amongst the visitors were Messrs. F. A. taken, the one to prevent the unevenesses being weakened and damaged by the opera- Klein, N. P. Burgh, J. Manners, A. Yarrow, and asperities which are produced upon that tion. Most of the steel rails rapidly coming portion of the rail in contact with the chair; into extensive use are of the double-headed the other, to enable the upper head, after form. In this, as well as in other similar being worn, to bed evenly and steadily in the matters, engineers must be guided by their chairs. With the ordinary chair these con- own experience and judgment; and where the ditions are not accomplished. The wooden merits of either side are pretty evenly balanced, keys which are employed to wedge the rail as in the present instance, we must expect to against the chair allow a small separation to witness advocates upon both sides. exist under the varying circumstances occasioned by the influence of the weather. sequently, the passage of a train produces a successive repetition of little shocks or concussions, which give rise, after a certain length of time, to a notching in the lower head of the rail which rests upon the chair. M. Séverac, a French engineer, proposes to obviate these difficulties by the adoption of a chair differing but very slightly in its construction from those in ordinary use.

FIC.I.

B

Con

FIG. 2.

In

THE NEW SWIVEL BRIDGE AT
BRISTOL.

patriotic toasts had been given and heartily Blundell, &c. After the usual loyal and responded to, the toast of the evening, "Success to the Society," was proposed. The the Society, which it may not here be out of response brought out some facts concerning place to reproduce. First, then, we learn that the Society has been in existence for nearly ten years, and now consists of twelve honorary members, nine life members, and seventy-five ordinary members. Its meetings are held on the second and fourth Wednesday in each month, from October to June incluNEW swivel bridge was opened last sive. The next meeting will be held on the month at Bristol, and which possesses 11th inst., when a discussion will take place the bottom of Clare-street, and opens on to which we purpose placing before our readers some noteworthy features. It is placed at upon the President's address, an abstract of St. Augustine's Parade, a point where a bridge next week. The papers read are purely of has always been necessary. Formerly, a a scientific character, and the Society are wooden lifting or drawbridge stood there, about to take steps to publish their proceedwhich was in time replaced by one of im- ings. This association also possesses an inner proved construction. This in its turn gave element, which renders it of especial value way to a still better design-a swivel bridge to the younger members. A species of inter-by Mr. Gravatt, C.E., which, however, at communication is carried on amongst the length became dilapidated, and has now been members through the secretary, and at any succeeded by a newer and more commodious meeting a member requiring information structure from the designs of Mr. Howard, upon any knotty or doubtful point, places engineer to the Docks Committee. To have his question in the hands of the secretary, placed the bridge so oblique as to have been who elicits an answer from the meeting, withexactly in line with Clare-street would have out, of course, divulging the inquirer's name. figs. 1 and 2 are shown the intended alterations. required the present pier of masonry re- On the whole, the Civil and Mechanical EnThe chair differs from that in common use by moved, and a new one built, and would, more-gineers' Society is a highly useful institution, having the size of the part B, in which the over, have placed the traffic towards St. and one which is well calculated to promote rail is bedded, larger, thus permitting the Augustine's-place at a great disadvantage. the interests of young aspirants to profeshead of the rail when turned to bed in it. A mean line, keeping the centre of present sional fame, being governed as it is by gentlealthough it may have become flattened and pier, was therefore adopted. In the present men of experience and sound practical knowlaterally increased in dimensions by the wear design, the system of a king post and sus- ledge. and tear it has undergone. In the chair, and pending rods, which gave the necessary underneath the rail, is placed a small cushion strength, but which took up a considerable C of hard wood, which is changed for another width, has been discarded, and the whole surof a slightly increased thickness when the rail face made available for traffic. The roadway is turned. By this arrangement, the rail will has been increased 1ft. 4in., and each of the always be securely and firmly bedded, and the footways 11in. in width. The total weight shocks will be avoided, which frequently break of the bridge, with its counterbalance, is the chairs, and occasion a large amount of about 120 or 130 tons, which is carried partly unnecessary wear and tear to the permanent on four cast-iron chilled wheels running on way and rolling stock. It is true that the an iron roller path, the crown of which is of shocks will still occur, but as the rail is bedded cast steel. The greater portion of the weight upon an elastic material, they will not have is, however, supported by the centre pivot, any injurious effect. The cushions of wood on the top of which are fitted gun metal and should be treated with some preserving sub- steel discs, and on these the bridge turns. In stance, such as creosote, and also subjected order to adjust the height of the bridge to to a pressure, to condense and harden them. any settlements or wear in the adjoining They will in that state still possess a degree roadways, the centre bearing on the metal of elasticity sufficient for the purpose, and dises is formed of a large hammered scrap iron be able to withstand the pressure and vibra- screw, 11in. diameter, by which the whole tion of the rail without being crushed or bridge can be raised or lowered. The old bridge altered in shape. The plan of introducing took six men about two minutes to open or an elastic medium between the rail and the shut; the present one, in which the friction is chair has been frequently tried, but it cannot reduced to a minimum, will take two men

EXPERIMENTS ON ANEROIDS.

[ocr errors]

THE 100 coins an accountoyal Society (No. 103) contain an account of certain experiments on aneroid barometers, made at Kew Committee, by B. Stewart, LL.D., F.R.S., &c. Observatory, at the expense of the Meteorological We propose to place before our readers an abridged report of these experiments, and then to add a few remarks of our own. In judging of the value of an instrument, says the report, such as an aneroid, it is not the mere extent of difference between its indications and those of a standard barometer that ought to guide us; but it is rather the constancy of its indications under the various circumstances to which it may be subjected, that determines its value. An aneroid may differ from standard barometer at the ordinary pressure, and vided these differences can be well ascertained to a greater extent at other pressures; but proand remain constant, such an instrument ought to be regarded as valuable, just as much as a chronoineter of known constancy, but of which the rate is wrong.

a

The circumstances which may be supposed to affect the indications of an aneroid may be classed under three heads, namely:

1. Time.

2. Temperature.

3. Sudden variations of pressure. 1. Time. Of the influence of time, Dr. Stewart has no definite information to communicate; therefore, of course, what he does actually say is of no value.

2. Temperature. A good aneroid is generally compensated by its maker for the effects of temperature, and the question to be investigated is, to what extent such compensations are trustworthy. I record the results of subjecting six aneroids, each 4in. in diameter, made by two different makers, to a very considerable range of temperature.

[blocks in formation]

These results are, on the whole, very satisfactory, and appear to show that a well-made compensated instrument has its indications comparatively little affected by a very considerable tem'perature change. It ought always to be borne in mind that an aneroid is not capable of being read to the same accuracy as a standard barometer, and that the 1-100th of an inch is a very small quantity. These temperature experiments were made at the ordinary atmospheric pressure. I am unable to say what effect a change of temperature would have at a diminished pressure.

3. Sudden changes of pressure.-For the purpose of investigating the influence of sudden changes of pressure upon the indications of aneroids, I applied to some of the best known makers of these instruments, for the loan of several, and through their courtesy in lending me a sufficient number, and for a sufficiently long time, I have been enabled to investigate this influence at some length. In the following experiments, the instruments were, to begin with, suspended vertically, at the usual atmospheric pressure. They were tapped before being read. The pressure was then lowered an inch, and the instrument allowed to remain ten minutes at this pressure before being read, after having again been well tapped. The pressure was thus reduced an inch every time, being allowed to remain ten minutes at each stage; the instrument was always well tapped before being read, by means of an arrangement contrived for this purpose by Mr. R. Beckley. The exhaustion was carried downwards to 19 inches, and the instrument was allowed to remain an hour and a-half at its lowest pressure; the air was then admitted an inch at a time, the previous arrangement as to time and tapping being followed.

Separating the results of the experiments into two sets, one comprising large (4in. to 4 in.) aneroids and the other small instruments, we find the mean down correction to be as follows, each aneroid being supposed right at 29in.

Mean correction) of two large aneroids....

Mean correction)

for four small
aneroids

2. That small aneroids are less trustworthy than large ones, and probably cannot be trusted below 26 inches.

3. That if previous experiments are made upon an aneroid, we are enabled by this means to obtain a table of corrections which, when applied to future observations with the same instrument, will most probably present us with a much better result than had we not verified our instrument at all, and that by this means we may use our instrument down to 19 inches with very good results. Readings of these instruments under increasing pressure, after remaining an hour and a-half at the lowost reading, were recorded.

The mean corrections for up readings are exhibited in the following table, each aneroid being supposed right at 19 inches:

[merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small]

We may learn from these results, says Dr. Stewart, that if aneroids which have been subjected for at least one hour and a-half to the lowest pressures which they register, have the pressure increased by means of the gradual introduction of air into the receiver, after the manner already described:

1. That a well-constructed large aneroid will not go far wrong for about 8 inches above the lowest pressure.

2. That in this respect small aneroids are somewhat less trustworthy than large ones.

3. That if the instrument read be previously tested and its corrections ascertained we may con

[blocks in formation]

We see from these results, says Dr. Stewart, that if aneroids, right to begin with, be subjected to a decrease of pressure similar to that to which they were subjected in these experiments

1. That a well-constructed large aneroid will not go far wrong down to 24 inches, but after that pressure its reading will be considerably lower than that of a standard barometer, so that a large positive correction will have to be applied.

sider it trustworthy (making use of these corrections) for up readings throughout a greater range than if it had not been so tested.

I come now to consider whether a rapid change of pressure affects an aneroid after the experiment has been completed.

[blocks in formation]

It thus appears that if an instrument reads correctly before it is put into the receiver it will read too low immediately afterwards, and that it may be some considerable time before it recovers its previous reading. The instrument cannot, therefore, be safely trusted for absolute determinations if it has been recently exposed to rapid changes of pressure.

The experiments hitherto recorded, in which an inch of pressure has been taken away or added every ten minutes, are perhaps analogous to ascents in a balloon, or descents from a mountain; they are not, however, precisely analagous to mountain ascents, since a longer time than ten minutes is usually taken to produce a change of pressure equal to one inch.

At the suggestion of Mr. Charles Brooke, a couple of aneroids were tested in April, 1868, with the view of rendering the experiment more analogous to a mountain ascent.

The pressure was reduced by half an inch at a time and at intervals of thirty minutes, the aneroids being well tapped.

The following corrections were obtained for down readings (instruments supposed right at thirty inches).

[blocks in formation]

From all these experiments, Dr. Stewart concludes as follows:

A good aneroid of large size may be corrected for temperature by an optician, so that the residual correction shall be very small.

If an aneroid correct, to commence with, be used for a balloon or mountain ascent, it will be tolerably correct for a decrease of about 6 inches of pressure. A large aneroid is more likely to be correct than a small one.

The range of correctness of an instrument used for mountain ascents may be increased by a previous verification, a table of corrections being thus obtained.

If an aneroid have remained some time at the top of a mountain, and be supposed correct to start with, then it will give good results for about 8 inches of increase of pressure.

A large aneroid is more likely to be correct than a small one.

likely to give a better result. If the aneroid has been previously verified, it is

After being subjected to sudden changes of pressure, the zero of an aneroid gradually changes, so The following table will exhibit the results ob- that, under such circumstances it ought only to be tained in this direction;used as a differential and not as an absolute instru

ment, that is to say, used to determine the distance ascended, making it correct to begin with, or to ascertain the distance descended, making it correct to begin with, it being understood that the instrument ought to be quiescent for some time before the change of pressure is made.

The results to which these experiments appear to have led are certainly interesting, but they throw no new light upon the action of the aneroid. All the peculiarities pointed out in this account have been long known, and have been stated over and over again. They are too perplexing for the generality of people to trouble themselves about, and the consequence is that the aneroid for common purposes holds a similar relation to a barometer that a Dutch clock does to a regulator. Among thoughtful persons, however, these results thus enunciated will produce good effect, and they well deserve the attention of the manufacturers of these instruments. It is a matter of regret that Dr.

the telescope by a tube of india-rubber. The
eclipse has been successfully observed in a clear
sky, further east than India, by M. Stéphan, a
French philosopher, who stationed himself at Wha-
Wen, in the Malayan peninsula; also by Captain
Reed, who observed it on the coast of Borneo. We
can hardly expect news from a more eastern district
still, as the island of Papua is too far from civiliza-
tion, and it is not easy to effect a landing on large
portions of its coast, because they consist of long
banks of mud, almost perfectly flat.

quantity of the solvent on the outside of the support; place the plate, collodion side upwards, on the ring, cover the box as nearly air-tight as possible with a piece of glass, and place it in a water bath; the vapour of the solvent will soon cause the varnish to swell, and the edges of the cracks to coalesce. As soon as this end in view is accomplished, the plate is carefully withdrawn, and when cool is again varnished with a similar varnish."

NOTES ON RECENT SCIENTIFIC DIS-
COVERIES AND THEIR PRACTICAL AP-
PLICATIONS.

STRONG STONE CEMENT-USES OF LIQUID AMALGAM
OF ZINC IN GALVANIC BATTERIES-BRANDY FROM
ICELAND MOSS-ANALYSIS OF WATERS.

N

Stewart did not examine the efficacy of the com- William Huggins, F.R.S., in obtaining the spectra A easy method, by which the amount of light

pensation for lower temperature and also under a low pressure.

It would not have been difficult to have constructed an apparatus suitable for the purpose. As regards the mere error of graduation, it is probable that, if the aneroids had all been placed with the dials horizontal during the investigation, a quite different set of corrections would have been obtained. It is, therefore, an omission of some moment not to have observed at all how the instruments indicated in horizontal as well as the vertical position. Why they were always tapped before being read is not stated. We are at a loss for any reason for tapping them. In our opinion, it is unnecessary and injudicious. Neither is it stated whether or not the aneroid readings were compared with the standard barometer readings corrected for temperature. If not, then the increasing error for decrease of pressure is partly accounted for; but, if they were, then it seems that the makers had not graduated them to accord with barometer indications corrected for temperature. As this is what should be the practice, if it is not followed, it

Direct photographs of the sun and its spots are taken regularly at Kew Observatory and preserved as records; some also, on a very large scale, have been taken by Mr. Warren De La Rue, F.R.S. Very beautiful fac-similes of the best of these pictures A MODE OF MEASURING THE INTENSITY OF LIGHT—A have been drawn upon steel plates, and are now published in a new and very good work on astronomy, by Mr. Norman Lockyer.* The same book contains descriptions of the apparatus used by Mr. of the stars, with illustrations. Much care has been may be at any time measured and registered, taken in getting up this standard little work, the is still wanting. Dr. Roscoe proposed, a year or author having been aided by several leading philo- two ago, to measure and register the intensity of sophers experienced in the several branches of the light by means of photography. This is, however, science. The Royal Astronomical Society placed facilities at his disposal; so also did Mr. Warren De rather a measure of the chemical activity of light La Rue and Dr. Balfour Stewart, Superintendent of than of light itself. Mr. Kirkham has proposed the Observatory of the British Association at Kew. the same means of measuring the luminosity of a Some recent photographic experiments by Mr. gas flame. But this, again, is objected to, since George Dawson, M.A., of King's College, are of the light of gas is deficient in the chemical rays. scientific interest. Three ounces of clippings from The simple instrument which has been devised by a bar of perfectly pure silver were dissolved in Mr. Roger Wright, and has been recently described pure nitric acid, and the slight excess of acid in the "Proceedings" of the Royal Society, will serve removed by recrystallizing the salt many times, excellently well to measure approximately the infrom the purest of distilled water, over a sand tensity of total daylight for comparative purposes. bath. A negative bath was then made of this It consists of a solid rod of metal standing perpenvery pure nitrate of silver, which proved to be dicularly on a heavy base. The top of the cylinder very slightly alkaline to test papers, a peculiarity is painted white, with a black spot in the centre. always exhibited by this salt when it is absolutely A hollow tube, blackened inside, is made to fit pure. A plate was coated with an ordinary exactly, and slide over this rod. slightly acid bromo-iodized collodion, and sensitized marked with a scale beginning with zero at in the bath. On trial in the camera, a foggy and the base. To use the instrument, the tube scarcely visible picture was the result, yet the is pushed over the rod down to the zero point; same collodion worked well in other baths. He it is then drawn gently up, the observer Those who use the aneroid for scientific purposes, then tried a very new and neutral sample of looking steadily at the black spot, and when the as for measuring heights, should never place much bromo-iodized collodion in the pure bath. This spot vanishes in the gloom the point is read off on confidence on its accuracy. Its indications require gave good and blooming negatives with an almost the graduated scale. The point will, of course, to be checked frequently with a standard barometer instantaneous exposure in the glass house. That vary with the intensity of the light, and thus a at the standard temperature, 32deg. Fah. The a neutral collodion and slightly alkaline bath measure of the intensity is obtained. errors of an aneroid are greatly more capricious should give good pictures is something entirely than the rate of a chronometer. Even to state new to photography, though the principle was that the aneroid may be used as a differential in- once laid down in a very unconvincing and comstrument is fallacious, or we do not know what is plicated manner by Mr. M'Lachlan. The same meant. It is not at all uncommon to find aneroids new and neutral collodion did not give good reading half an inch wrong. To suppose such an pictures in the ordinary acid baths. If, after instrument correct, when determining by it differ- further testing, these facts should be verified ences of elevation, is to suppose that equal differ- beyond all doubt, the discovery will be valuable in ences of pressure throughout the atmosphere are astronomical photography, for the slight trace of exponents of equal differences of elevation, which acid usually given to secure clean pictures has slight retarding influence, and necessitates a slightly longer exposure.

ought to have been inculcated.

is not true.

PHOTOGRAPHY.

THE GREAT ECLIPSE OF THE SUN-ASTRONOMICAL
PHOTOGRAPHY-ALKALINE SILVER BATHS-IN-
STANTANEOUS PHOTOGRAPHY-CRACKS IN NEGA-

TIVES.

SINCE the first news reached England of the

a

The rod is

Böttger informs us that a cement of extraordinary binding power is made by using infusorial silica in place of quartz sand. This infusorial earth is found in Germany only, but it has been imported into this country in considerable quantities. It consists of hydrated silica, which combines with bases much more readily than silica in the anhydrous condition, as in quartz sand. The infusorial silica is mixed in about equal proportions with oxide of lead; about half a part of freshly slaked lime is then added, and the whole is made into a paste with boiled linseed oil. The cement thus made quickly becomes as hard as sandstone, and will be found extremely useful in such work as fixing iron in stone for balusters and railings. It is not likely, we think, to expand in setting, and thus no risk of splitting the stone will be incurred. In this respect alone it offers a great advantage over Portland cement, sometimes used for the purpose we have mentioned, which, according to some authorities, does expand, and in consequence of which one very serious accident is supposed to

have resulted.

In rapid photography, where the exposure requires to be reduced to the smallest possible fraction of a second, slight influences like these have their weight, yet the value of these influences is not scientifically and accurately known. Celestial photography will not be brought to perfection till many obscure phenomena of this kind have their work of Major Tennant, R.E., in photograph-accelerating and retarding powers determined by accurate experiments. Under all ordinary circuming the total eclipse of the sun at Guntoor, he has stances, these slight influences are unnoticed and made enlarged copies of some of the negatives then unknown, because they do not interfere appreciably obtained. Although, as we have previously stated, with the results. Fortin has recently proposed to use a liquid the original negatives were faulty, still some of Many bad photographic varnishes constantly amalgam of zinc in galvanic batteries in place of creep into the market, and some of them have a that metal alone or only superficially amalgamated. them not only show the flame prominences, but most disastrous effect upon the pictures, cracking The advantages are said to be a saving of the streaks in them, spiral in form. Dr. Vogel, who valuable negatives all over, and rendering them trouble of shaping the zinc, and greater constancy very successfully photographed the total phaso at worthless. We know an amateur photographer of power from the ease with which the sulphate of Aden, used a bromo-iodized collodion, which also who, after a tour of a few weeks in Wales, taking zinc can be removed as it is formed. We are not pictures of beautiful sea coast scenery, had half yet told the exact way in which the liquid amalgam contained an excessively large proportion of alcohol, his negatives cracked all over by a miserable is disposed, but as soon as we receive the informato render evaporation less rapid in a tropical climate sample of varnish. When such cracks are very tion we shall give it. than if the collodion contained the usual amount of fine, the negative will sometimes print well if a little plumbago be gently brushed into the cracks.

ether. He also used nothing but cadmium salts in In Kingham's work on photography we find the and, from that, brandy, from lichens. Iceland moss,

following little-known remedy for the evil, and if
it really answers in practice, it must be
valuable:"First ascertain whether the solvent

very

Among the curiosities of chemistry we may mention the production in Sweden of grape sugar, the collodion. The developer consisted of ammoniosulphate of iron 7 parts, acetic acid 5 parts, and for example, which is found in Sweden in large quantities, contains a good deal of starch, which, water 102 parts. Of the three plates exposed, one as well as the cellulose, is converted into grape gave a perfect image, the second was a little under- of the varnish on the plate be alcohol, chloroform. sugar by boiling with a dilute acid. A specimen exposed, and the third was a failure because of the passage of a cloud at the moment. A long sliding or benzole, by dropping on one corner a minute of Iceland moss gave as much as 72 per cent. of back was used in the telescope camera, to allow drop of each of these menstrua, to ascertain which glucose, which, when fermented and distilled, two pictures to be taken on one plate, so that he what larger than the picture, about lin. deep; at dissolves the varnish. Next take a tin box some- yielded a brandy having a very agreeable flavour. It will be interesting as well as novel information really obtained six pictures of the eclipse, two of the bottom of this box solder a ring of tin, about that M. Bechamp considers he has established that to chemists concerned in the analysis of waters which were failures. The photographic parts of his apparatus were not directly attached to the in. wide, of the same shape and nearly of the same in sulphuretted waters, containing, as they suptelescope, because the insertion of the slides might size, as a support for the glass plate; pour a small alkaline sulphides, the sulphuretted hydrogen otherwise set up vibrations, so the camera was fixed upon a separate stand, and connected with LOCKYER, F.R. A.S. London: Macmillan and Co, 1868. "Elementary Lessons in Astronomy." By J. NORMAN and the alkali are not in combination, but remain free, although in the presence of one another.

pose,

[subsumed][merged small][graphic][graphic][merged small][merged small][graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small][graphic][graphic]
« EelmineJätka »