LA ROYAL ASTRONOMICAL SOCIETY. The President, in his opening address for the session, said that the late eclipse in India had been observed most satisfactorily, and that the gentlemen who had been despatched on the mission had fulfilled all expectations in every way, every expedition having been most successful. More especially have the efforts of Mr. Norman Lockyer and Dr. Janssen been of public value. For many years past astronomers and physical philosophers have been examining the constitution of the sun, such, for instance, as Messrs. De La Rue, Balfour Stewart, Miller, and Huggins; but the grand keystone of the arch has just been put in by Mr. Norman Lockyer and Dr. Janssen. The British Association gave opportunities to their members at Norwich to show what they had done, and many members of the Royal Astronomical Society "came out," including Mr. Burt and Mr. Glaisher, and others, helping in work relating to the moon. He hoped that the Society would hereafter receive much reliable scientific information from distant parts of the globe. A gentleman told him a few days ago that he was going to establish an observatory at Nankin, in China, and promised to send in some results. He (Admiral Manners) thought that perhaps from observatories lying far to the east the Society would in future get interesting accounts of meteoric showers. NOTES ON RECENT SCIENTIFIC DIS-larly laid before our readers the progress of dis-read two reports of observations of the eclipse made PURE SILVER AND ITS PROPERTIES-A NEW DIS- IN TIN AND TINNED VESSELS. ME ETALS are rarely seen in a state of absolute purity, and as very small amounts of contaminating substances considerably modify their physical properties, and to some extent also their chemical behaviour, the characteristics of pure metals are but little known. Our knowledge of silver has recently been considerably extended by the experiments of Professor Christomanos, of Athens, who has obtained the pure metal by distillation. Silver was well known to be volatile to a slight extent at very high temperatures, but the Professor, by the use of a sort of bullet mould made of well-burnt lime, into which he could direct the is sufficient to fill up the bore with sand. Gun driven by good clockwork, and furnished with an Venus crosses the disc of the sun. Professor G. B. Airy, the Astronomer Royal, said that he believed that the last transit of Mercury had been botter observed at Greenwich than anywhere else, for there six telescopes were brought to bear upon the phenomenon. Mr. Stone was stationed at the great equatorial, a fine instrument, object-glass 13in. in diameter. Moreover, it supports the observer in a comfortable position, and that is a very great thing. Mr. Stone did not attend to time, that work being left to other observers. Just before the last contact he saw the phenomenon known as the "black drop," in appadirection of the limb of the sun. This phenomenon rent elongation of the disc of the planet, in the is probably caused by irradiation, and he thought might be thus explained:-Let B B in the accom Mr. William Huggins, F.R.S. (secretary), then of the Royal Arsenal, Woolwich. As we have regucovery with this important explosive, we need only by captains in charge of ships belonging to the Peninsular and Oriental Steamship Company. recal the last stages-the preservation from decomA discussion then took place upon the recent position by the use of a weak alkali, and the employment of compressed charges. Used in the last-transit of Mercury across the disc of the sun, mentioned form, we have said that gun cotton, which transit had a special value to astronomers, lighted by an ordinary fuse, has about six times because an accurate timing of the contacts by good the destructive force of an equal weight of gun-observers gives data for more exact computations powder. Messrs. Abel and Brown, however, after as to the real distance of the sun from the earth. experimenting with gun cotton saturated with Some future transits of Venus will be more valunitro-glycerine, igniting it necessarily with the able in this respect than transits of Mercury, but detonating fuse, tried the experiment of igniting the movements on such occasions of the latter showed that cotton exploded in this way has, per-work they will have to do in a few years, when gun cotton alone in the same way. The results planet presents some peculiar phenomena, and its transits help to get observers into practice for the haps, greater destructive force than nitro-glycerine. This is a great and valuable discovery, for we have here the comparative safety of the gun cotton with the tremendously destructive powers of nitro-glycerine. For mining and quarrying purposes it removes the only source of danger from the use of gun cotton, for no hard tamping is necessary. I cotton, as we have recently shown, may be carried flame of an oxyhydrogen blowpipe, was enabled to and stored with perfect safety from explosion. The obtain enough of the metal to experiment with. detonating fuse can be inserted in the charge when The pure metal he describes as of dazzling white- it is required for use. As with nitro-glycerine, the ness. Its specific gravity is 10.575, which is a explosion of one charge provokes the explosion of another. Thus, if it were required to detrifle higher than that usually given. It is, of stroy a stockade, it is only necessary to place course, easily soluble in nitric acid, and in hot con- the charges at distances round the enclosure, centrated sulphuric acid. In extremely thin layers and explode one. The explosion of all follows it shows by transmitted light a bluish green colour; with instantaneous rapidity. Moreover, as said in somewhat thicker, from a yellow to a yellowish above, when the cotton is exploded by the brown colour. In the first case, it allows the che- detonating fuse, it is not necessary to confine it. mical rays of light to pass, as the Professor proved Just as with its analogue, nitro-glycerine, the exin an original way. Chemically pure silver he plosion is so instantaneous that the shattering finds is easily soluble in a hot solution of cyanide effects are just as great as when the chargo is of potassium. When in such a solution, heated to quito exposed. Large blocks of granite, and thick 60 or 70deg. C., a glass rod heated to a somewhat plates of iron have been shattered by exploding higher temperature is immersed, an uniform layer open charges upon them. A detailed account of of metallic silver is deposited, which becomes the experiments made by using gun cotton in this thicker the longer the rod is allowed to remain in the way is not yet made public; but the discoverers solution. By filling a test tube with mercury heated will, no doubt, soon supply it. to 110deg. C., and immersing it for a moment or two in the solution, a dull white coating of silver was deposited on the outside, which on the inside was seen as a brilliant silver mirror. The tube was then filled with equal volumes of hydrogen and chlorine, and carried into [sunlight, whereupon combination and explosion took place. In the case of a tube left in the solution for a longer time for a thicker layer of the metal, and filled with the same gases, combination only took place slowly and without explosion. It may be that the mode of silvering glass above described may be utilized for the silvering of glass globes and other ornamental objects, which are now silvered by the somewhat complicated reduction processes. A great discovery in connection with gun cotton has been made by Professor Abel and Mr. Brown, A report has been published on the tin and tinned vessels used in the military hospitals in France. The metal used for tinning it was found contained from 25 to 50 per cent. of lead. In vessels reputedly made of pure tin, the Commissioner found, in some cases, as much as 15 per cent. of lead. Such proportions are dangerous, he says, to the public health, and the Government is recommended to fix a standard allowing only 5 or 6 per cent. of lead to be used with tin in utensils intended for culinary purposes, or for drinking vessels. The author has probably overstated the dangers from the use of utensils composed as he has found; but it would be well if cheap manufacturers in this country would bear in mind that it is not altogether safe to use a large proportion of lead. H AB EF panying drawing be the real Bedge of the sun, and let A A be the apparent limb of the sun as enlarged by irradiation. Again, let the outer small circle F be the true disc of Mercury, and the inner small circle E be Mercury as it appears to the eye when diminished in size by irradiation. Now, when the real edge of Mercury touches the real limb of the sun, there is not enough light left at that place to produce irradiation because of the cusp that is formed; consequently, there is an apparent elongation of the planet, as shown at H, and this is the true contact. In past years, people were very much perplexed by this phenomenon, and his own early idea on the point was that the observers used very bad telescopes; but he soon had to give up that theory. Irradiation is probably a purely ocular phenomenon, having its seat in the eye itself, and will, therefore, be unavoidable to the end of time. In 1874 and 1882 there will be transits of Venus, for which transits all astronomers should prepare beforehand. It will be important to consider all these things, and to lay down rules as to the character and quality of the instruments to be used, and the instructions to be given to the observers. He did not observe the transit of Mercury himself, because he knew that he had persons about him younger and better able to do the work. He did look at the planet while it was on the sun. There is one thing which should be attended to very carefully by astronomers, and that is that all observations to determine the parallax of the sun must be made when the sun is low down towards the horizon, and the planet must appear to be on the high side of the sun to one observer, and on the low side to the other observer, otherwise the measurements will not be valuable. Glass which gives a red tinge is bad in the telescope, because it gives a spectrum. The best thing to reduce the light of the sun he thought to be a darkened glass, which gives a green tint, since this gives very little of the atmospheric spectrum. Would it not be possible to introduce a prism into the eyepiece, and introduce dispersion opposite to the atmospheric dispersion? The President said that it was a good thing that Professor Airy came forward, as hitherto astronomers had been left much to their own ideas as to the real time of first contacts. Mr. James Buckingham, F.R.A.S., said that during the transit of Mercury he made fifteen double measurements of the disc of the planet. He used two telescopes, one with a 9-inch and the other with a 21-inch object glass. The planet was considerably smaller than described in the "Nautical Almanac." He timed his observations with a chronograph. Mr. William Huggins, F.R.S., said that he observed the transit of Mercury with an 8-inch telescope. He saw a bright spot on the planet, which disappeared when Mercury went off the disc of the sun. If Mercury be surrounded by an atmosphere turning aside the beams of the sun, it might produce the effect. Other observers than himself have seen the bright spot in past years. Mr. Huggins then read another paper upon old transits of Venus. Mr. E. J. Stone, F.R.A.S., then made an elaborate defence to an attack upon a recent paper of his own, wherein he had demonstrated that the observations of the transits of Venus in former times had been made with considerable accuracy, but that astronomers had made grave errors in their calculations founded upon the observations. These errors in calculation were the causes of the mistake which had so long prevailed as to the real distance of the sun from the earth. He did not know whether there was anything of e the sun itself was spread out into a nearly continuous spectrum. Professor Adams agreed with the explanation given by Mr. De La Rue. Mr. Lockyer said that two slices of light only, one above the other, were admitted through the slit of the star spectroscope. One of these, from the limb of the sun, was spread out into a long broad spectrum, but the other into three or four bright lines only. Thus the relative brilliancy of the two lines was altered. Mr. Stone.-Yes. You disperse one more than the other. Mr. J. Norman Lockyer, F.R.A.S., said that, in 1866, he communicatod a paper to the Royal Society, about the application of spectrum analysis to the determination of the physical constitution of the solar spots. He succeeded to some extent, and then thought that perhaps it was possible to examine by this method the prominences on the limb, without waiting for an eclipse. The means at his disposal were limited, and the results unsatisfactory. He told Mr. Stone so, who also was Mr. William Huggins said that he had often had trying the same thing. The Royal Society then a search after the prominences with his spectrogave him the means to construct a larger instru- scopic apparatus, but without success. He now ment, with which, on the 20th of last month, he thought that his spectroscope gave too much disobtained a sight of the lines of one of the promi-persion for the purpose, for he knew not where to nences. About two months before Dr. Janssen did look for the lines, and the apparatus would only the same in India. On the 5th of November he show a little bit of the spectrum at a time. In(Mr. Lockyer) made a more important observation. stead of using a prism, he once tried the interThe instrument had then had some improvements position of media to cut off some of the surplus made in it by Mr. Browning, and upon turning it light, and shut out those parts of the spectrum not to th limb of the sun he was surprised to see, wanted. Now they knew where the lines were dir y he looked through the eye-piece, a pheno- situated, perhaps the plan might be of some use. mea ich somewhat puzzled him. He saw not He found one specimen of dark ruby glass which a lon] ae, but a short one, which appeared to in- cuts off all the rays down to between D and C, and dicate mall prominence, or a loop of a large one. which would be very likely to let the line C be Yet thigh he swept the limb of the sun for some time, fra distance of, perhaps, 200,000 miles, he could nd no large prominence, but still saw the shot lines. He concluded, therefore, that they camerom a gaseous envelope of the sun altogether new to science. He obtained the same results in every part of the limb of the sun, except where there were prominences. Thus is indicated a new envelope five or seven or eight thousand miles in height, extending all round the sun. There is no great difference in its thickness at the poles or at the equator. The reports from India give three lines as those most generally seen. It was the same with himself. But when the action is excessive he sometimes saw a fourth line, near the c of the scale. The spectrum of the sun itself is always visible in the instrument at the same time as the spectrum of the prominences. seen. The Astronomer Royal said that he had considered Mr. Warren De La Rue's explanation, and now thought it quite satisfactory. The proceedings then closed. MINERALS AND METALS. THE production of coal in the United Kingdom United States is said to be estimated at about in 1867 reached 104,500,480 tons; that of the 25,000,000 tons. Nearly one-fourth of the coal raised in the United Kingdom comes from the Durham and Northumberland coal-fields. There were 2,871 collieries in the United Kingdom in 1857, and 3,258 in 1867; in 1857 the entire production of coal from them was only 65,394,707 tons. The following statement shows the value of the Mr. Babbage asked whether an artificial eclipse minerals raised in the United Kingdom in 1867 :— of the sun could not be made at will by suspending Coal, £26,125,145; iron ore, £3,210,098; tin ore, some round opaque body in the telescope? £624,734; copper ore, £699,693; lead ore, £1,158,066; Mr. Newall (who spoke from the midst of a The Astronomer Royal said he could not under-zinc ore, £41,340; iron pyrites, £67,453; gold crowd of members standing in the doorway of the stand why the prominences could not be seen with-quartz, 3,241 tons, £5,320; nickel ore, £14; arsenic, room), said that he and his neighbours were like out the aid of spectral dispersion. Some years ago, Shadrach, Meshac, and Abednego of old, for they when the prominences were a great deal under stood at the mouth of a burning fiery furnace. discussion, he told Mr. Nasmyth his desire to reWould the President act the part of Nebuchad-ceive an image of the sun, in a dark room, upon a white card. This card was to have a round hole cut in its centre, through which the image of the sun was to pass in a black bag, and the prominences, it was hoped, would be seen on the card. Mr. Nasmyth then made him a ball and socket for the telescope, and they fixed their apparatus in a very dark hut. They then let the sun go through the hole in the white cardboard, and he expected to see red prominences without number upon the Yet he thought the conditions were very favourable, and he could not understand how it is possible to see the prominences with spectroscopic apparatus -it put him in a great puzzle. He did not say this to throw any doubt over Mr. Lockyer's discoveries. Mr. Stone and himself had resolved to see nezzar and bid them "come forth?" He was sur prised that the Royal Astronomical Society could not find a room big enough to hold its members. The President asked Mr. Newall how many members would attend at the next meeting of the Society? However, they would have a larger room in time, and near the platform there was plenty of room for Mr. Newall and his friends. Mr. Newall complained of the horrid ventila tion. Mr. William Huggins said that there was plenty of ventilation, only it was not very apparent. It was below, under the seats. A voice wanted to know whether the ventilation was all below, and none at the top? The Secretary then read reports of observations of the transit of Mercury, as seen in several British observatories. Mr. Birt then read a paper on the lunar crater Linné. The Astronomer Royal said he wished to call the attention of the Society to a now discovery of the constitution of a comet by Mr. William Huggins. For the moment he forgot the name of the comet, which was a small one, but Mr. Huggins had discovered by his spectroscopic researches that it contains carbon in a state of ignition. When he first heard the fact he thought it quite a new thing, and that no meteorite containing carbon had yet been found. Professor Miller had, however, told him of four meteoric stones which were found, upon analysis, to contain carbon in very sensible quantity. Here, then, is a little further connection between the formation of comets and meteors. Mr. Brayley said that many meteors contained carbon. Dr. Warren De La Rue said that he had in his possession a piece of meteorite containing carbon. Captain Noble, F.R.A.S., wished to call attention to a curious fact. That day was the 13th of November-a day on which great meteoric showers often fell, also a day when a great barometric wave runs up to its maximum. That day the barometer was at its maximum pressure for the whole month. white rim to the hole, but could not see one. to the thing again next summer. £4,112; gossans, &c., £5,808; wolfram, £62; manganese, £3,232; barytes, £7,807; coprolites, £70,300; salt, £836,963; clays, fine and fire, £589,650; earthy minerals estimated £650,000; making a total of £34,169,797. The value of the metals obtained from these ores in 1867 was as follows:-Iron, £11,902,557; tin, £799,293; copper' £831,761; lead, £1,337,509; zinc, £79,693; silver, 895.394oz., £215,400; gold, 1,520oz., £5,890; other metals, estimated, £15,000; making a total of £15,187,013. Adding £26,125,145, the value (at the place of production) of the coal raised, and £2,167,933 for other minerals not smelted, salt, clay, &c., the total value of the metals and coal and other minerals produced in the United Kingdom in 1867 is found to be £43,480,092. In 1866 the amount was £41,712,330. It is reported that the Black Hole of Calcutta has been at length discovered. No one has hitherto been able to ascertain the exact position of the dun on where so many of our countrymen perished in 1756. Conjecture pointed to a spot in the southern curtain of the old fort of Calcutta, which is now being pulled down; and here a space, the exact counterpart of the Hole, has been discovered by Dr. Norman Chevers, who has been on the look-out for the place for some years. Mr. Warren De La Rue said that the difficulty in seeing the prominences arises from the fact that astronomers do not throw out the illuminated atmosphere of the sun, so have to try to alter the relative brightness of the two lights. In the star spectroscope the whole of the rays from the limb of the sun are spread out over a large area, whilst the rays from the gases are brought together. He thought that perhaps it might be possible to photograph the solar prominences; that the light not wanted may be sifted away, and the rest allowed-A most interesting and instructive little work, to come through. During the eclipse in Spain the photographic eye could see what the human eye could not see. Perhaps a thinly silvered glass medium would do to cut off many of the luminous rays. N THE MANUFACTURE OF WATCHES AND CLOCKS. describing briefly, but with great clearness, the rise and progress of watch and clock making, has just been published by Mr. J. W. Benson, of 25, Old Bond-street, 99, Westbourne-grove, and the City Steam Factory, 58 and 60, Ludgate-hill. The book, which is profusely illustrated, gives a full descripThe Astronomer Royal said that he could not tion of the various kinds of watches and clocks, yet comprehend Mr. De la Rue's ex-with their prices, and no one should make a purchase planation. If a line A were without visiting the above establishments or consultlooked at through a spectrum it would ing this truly valuable work. By its aid persons give, say, for argument's sake, three residing in any part of the United Kingdom, India, fainter lines, B, In the same way, the watch best adapted for their use, and have it if they observed a flame or promi- sent to them with perfect safety. Mr. Benson, who nence, N, it would give, say, three holds the appointment to the Prince of Wales, sends fainter prominences, T. There- this pamphlet to any address on receipt of two fore he was still left in the dark. postage stamps, and we cannot too strongly recomMr. Warren De La Rue said that the light from mend it to the notice of the intending purchaser. B or the Colonies, are enabled to select for themselves The change from the square to the octagonal shape scale from the rolling mills at the works-it having been, in the first place, ascertained that the supply of iron scale could be furnished to the contractor with sufficient rapidity. The following are approximately the proportions of the ingredients of the mortar by measure: Lime Total 2 measures. 1 5 8 tank, &c., are also attached to this framework, and largely assist to counterbalance the load. The jib consists of two strong oak beams bound together, the radius of which is adjustable by a worm and It had previously been ascertained by observawheel. The boiler is multitubular, with an in-vation of the success and failure of actual chimneys, ternal fire-box, and contains 162 square feet of and especially of those which respectively stood heating surface. It is provided with two safety and fell during the violent. storms of 1856, that in valves, one of which is locked up; these valves are order that a round chimney in this country may weighted to 60lb. per square inch. The chimney be sufficiently stable, its weight should be such is hinged to the smoke-box to facilitate the clean- that a pressure of wind of about 55lb. per square ing of the tubes. The engine has two cylinders foot of a plane surface directly facing the wind, 7in. diameter and 10in. stroke. It is fitted with or 274lb. per square foot of the plane projection of It is scarcely necessary to state that the use of link motion. The valve rods are carried through a cylindrical surface that is to say, a pressure iron scale for hardening mortar and making it the casing, the extreme ends of the rods working equivalent to the weight of a layer of brickwork artificially hydraulic, is familiar to engineers, into brass bushes, which give them a much steadier 3in. deep, and of an area equal to the vertical sec- architects, and builders in Glasgow and its neighmotion when reversing quickly. The crane barrel tion of a round chimney-shall not cause the re-bourhood, but in many other parts of the country is driven by a spur wheel and pinion; a powerful sultant pressure at any bed-joint to deviate from that process appears to be less known than it friction brake for lowering is also provided, and the axis of the chimney by more than one-quarter deserves. The principal constituents of the iron worked by the foot. All the handles for starting, of the outside diameter at that joint. By calcu- scale are probably silica and protoxide of iron, but reversing, &c., are conveniently arranged, and of lating according to that principle the thicknesses its action upon lime, and the nature of the artieasy access. The swinging motion is performed of brickwork in the cone were determined to be ficial cement which it forms, have not hitherto, by steam, the arrangement being as follows:-A as follows:so far as I know, been investigated by chemists. cast malleable worm-wheel is securely fixed to the Considering the benefits that have arisen from the bottom of the central pillar, which gears with a chemical analysis of other cementing materials, worm shaft. This shaft is worked by two wheels, it is much to be wished that some chemist should has large bearings, and is otherwise of ample undertake the examination of this material also. strength. The clutch on the barrel shaft, which is of cast iron, malleable where geared with the spur wheel, makes the crane swing in either direction, the motion being altered by the reversing lever; all the bearings are brass. The pump is provided with a brass plunger, brass valves, brass feed cock, and is supplied from a tank on the foot-plate, the level of the water in which is above the pump, which invariably keeps the latter in good working order. All the necessary details to make the engine and boiler complete are previded. In our engraving, at page 433, separate drawings of many of the details are shown. CHIMNEY AT THE WEST CUMBERLAND Uppermost 80ft. of height.... Next 88ft. 14 brick. 2 bricks. The bed-joint of least stability is 2ft. above the At 2ft. above the ground line..... On the top of the chimney is a pitch-coated, cast-iron curb, lin. thick, coming down 3in. on the outside and inside. The lightning conductor is a copper wire rope, about in. diameter. It terminates in a covered drain, in which there is always a sufficient run of water. Tenders were taken from a limited number of In the construction of the internal scaffolding care was taken that the needles, or horizontal beams, should be supported wholly by the brickwork, and not by the upright posts; for great danger has been known to arise from the brickwork coming to bear upon the ends of the needles, and through them on the posts, owing to the settlement of the lower part of the chimney. In order that the concrete foundation might have time to harden before being subjected to a heavy load, it was made by the Iron Company themselves before The thicknesses of brickwork already stated known that intense pressure tends to retard the the contract for the chimney was let; for it is BY W. J. MACQUORN RANKINE, C.E., LL.D., &c. include the fire-brick lining, whose thicknesses THE chimney now to be described presents are as follows:-In the uppermost 160ft. of the hardening of concrete. The progress of the buildnothing new in design or construction, and cone, half brick; in the lower part of the cone, the ing was restricted by the specification to a rate is not of any extraordinary size or figure; but as it basement, and the flue archways, one brick. The not exceeding 6ft. of vertical height per day. is a successful example of the application of cor- fire-brick lining is bonded with the common brick-builders in the north of England and in Scotland; rect principles and good workmanship to a struc- work in the ordinary way-the only difference and the lowest offer was accepted, being that of ture of an useful and ordinary kind, the publica- being that the fire-bricks are laid in fire-clay and Messrs. William Wilson and Son, of Glasgow. The tion of an account of it may prove serviceable. It the common bricks in mortar. The reasons for work was executed by that firm in a manner that has now (April, 1868), been in operation for about adopting this mode of construction in preference left nothing to be desired. The following were the eight months, and has withstood the gales of an to an internal fire-brick chimney are as follows: amounts of the estimated and actual cost respecunusually stormy season. The duty which this First, when the fire-bricks are bonded with the chimney has to perform is to carry off the common bricks, they contribute along with the tively:-Engineer's approximate estimate, £1,672; gaseous products of combustion from four blast common bricks to the stability of the chimney; actual cost, including designing and superintendence, furnaces, and from various stoves and boilers that whereas if an internal fire-brick chimney had been £1,560; being at the rate of almost exactly fourare heated partly by burning the inflammable gas used, an additional thickness of common brick-pence per cubic foot of the whole space occupied from the blast furnaces and partly by coal. The work would have been required in order to give by the building, which is 94,000 cubic feet nearly. total quantity of solid fuel consumed may be esti- sufficient stability to the outer cone; second, inside the chimney, when doing about three-fourths According to the latest account, the temperature mated at about 10 tons per hour when all the unless the internal chimney is carried up to the of its full duty, is 490dog. Fah.; and the pressure furnaces are at work. Above ground the figure top of the outer cone, there is a risk of damage of the chimney is the frustum of a cone with a through the explosion of inflammable gaseous mix- of the draught is 12in. of water, which agrees to straight batter. Underground there is a plinth tures in the space between; and, third, under the a very small fraction with the pressure as deduced or basement, octagonal outside at the ground line same circumstances there is also a risk of the theoretically from the temperature and the height and square at the bottom; cylindrical inside, and cracking of the outer cone at and near the upper of the chimney. pierced with four circular openings for flues. The end of the inner cone through unequal heating which has just been described are nearly the same The dimensions and stability of the chimney reason for adopting a straight batter, notwith- at that place. Vertical cracks in a chimney are with those of the second highest chimney at standing that a curved batter enables certain the more dangerous the higher the level at which St. Rollox Chemical Works, built about ten years theoretical conditions to be more perfectly ful- they occur, because the safety of the higher part filled, is that the accuracy of building with a of a chimney depends more on cohesion and less previously, except that in the older chimney the straight batter can be tested at any moment by a on weight than that of the lower part. When such joint of least stability is 100ft. above the ground. glance of the eye without the aid of instruments. cracks take place near the ground, they are of In the great St. Rollox chimney, 445 ft. high The principal dimensions are as follows:- little or no consequence. The basement is paved wind which can safely be borne is almost exactly from foundation to top, the greatest pressure of inside with 6in. of fire-brick, resting on 6in. of the same, viz., 55lb. per square foot of a plane common brick, which rests on the concrete. Height above the ground line Feet. 250 17 267 Ft. in. 13 0 21 10 18 10 of archways for flues... 7 6 Outside diameter at top of cone......... 15 3 at 2ft. above bottom of 25 7 cone Outside dimensions of square course 30ft. x 30ft. Ft. in. Ft. in. 31 6 x 31 6 34 6 × 34 6 * Read before the Institution of Engineers in Scotland. Outside dimensions of concrete foundation The square foot of a plane surface, or 33lb. per squaro foot of the plane projection of a cylindrical surface, so that there it may be considered that there is an excess of stability. The ordinary brickwork is built of white bricks surface, or about 274lb. per square foot of the of very good quality, supplied by the Iron Com- plane projection of a cylindrical surface. pany. It is built in English bond: in the base-bed-joint of least stability is 210ft. above the ment there is one course of headers to every two 468ft. high from foundation to top, the bed-joint ground. In the great Port-Dundas chimney, courses of stretchers; in the cone, one course of of least stability is 200ft. above the ground; and headers to every three courses of stretchers. the greatest safe pressure of wind is 671b. per Strips of No. 15 hoop iron, tarred and sanded, are laid in the bed-joints of the cone at intervals of 4ft in height, with their ends turned down into the side joints. Care was taken to bed the hoop iron on the common brickwork, and not on the firebrick lining. The length of hoop iron in each bed-joint in which it is laid is twice the circumference of the chimney. In the concrete foundation, the basement, and a small part of the cone, the mortar was made of hydraulic lime. Owing to an unexpected difficulty in obtaining such lime on the spot, it had to be brought from a distance at considerable expense; and, therefore, the mortar for the rest of the building was made of a very pure lime from the immediate neighbourhood, rendered artificially hydraulic by a mixture of ion |
