APRIL 5, 1861.] THE LONDON: FRIDAY, APRIL 5, 1861. preliminary examination might be found ad- MECHANICS' MAGAZINE. even under our present system of patent law, THE NEW AMERICAN PATENT ACT. The principal points in the new American patent law which deserve notice at present relate to the preliminary examination of inventions, the fees payable for patents, their publication, and their duration. The system of preliminary examinations in the United States has been found so acceptable and useful that the new law provides additional examiners, classifies them, and authorizes the commissioner to appoint as many as may be required, "provided the whole number shall not exceed four of each class, and that the total annual expenses of the patent-office shall not exceed the annual receipts." British and other foreign inventors should clearly understand that American patents are not to be obtained, as in this and other countries, merely upon application. The American system of preliminary examinations compels every applicant for a patent to have all his papers "correctly, legibly, and clearly written," and to state exactly what is new in his invention. If he claims anything It that is not new, his patent is rejected. should be borne in mind also that one half of all petitions for patents suffer a first rejection, although many of these are afterwards granted upon revised papers, arguments, appeals, &c. In all cases of rejection, inventors are at liberty either to abandon their patent or, if convinced that their invention is new, to revise their papers, and prosecute their application; and the cost of appeal from the examiners-in-chief to the commissioner is only £4. This system compels the inventor to employ a well-qualified patent agent in the preparation of his papers, If the agent be and in conducting his case. not experienced, careful, and honest, the inventor is certain either to incur additional expense in rectifying errors and making appeals, or he may lose his patent altogether. So important is it that the papers should be carefully prepared, and that nothing except what is novel should be claimed, that it has become a separate and considerable part of the American patent agents' business to advise inventors regarding the probability of obtaining patents. For a fee of five dollars, accompanied with a model or drawing and description, an American patent agent will make a special search at the United States' Patent-office, and report upon the prospect of obtaining a patent. This voluntary 227 quantities are used in this country than in America, or in the treatment of raw materials, more extensively employed in our own manu factures. To counterbalance, this, however, there is the greater love, and the readier appreciation, of novelties in America. A new article, which must fight its way slowly in England for ten or twelve years before it is appreciated and patronized, will become, in half that time, popuIt must be gratifying to British inventors to lar and common in the United States. It is far know that the invidious distinction between easier to sell an American patent than an Engcitizens of the United States and subjects of lish one, and the former will, in most cases, the 500-dollar fee formerly required from value arises chiefly from the large and ready other countries is now abolished. Instead of bring much higher prices. This difference in British subjects, and of the 300-dollar fee from demand for improvements of all kinds, the restall others not citizens of the States, the sums less novelty-loving disposition of the people, and now payable by every person, no matter his na- their ability to buy ; also from the greater libetionality (excepting Canadians) amount, on ap- rality hitherto shown by the United States plying for a patent, to 15 dollars, and, on the Government towards inventors, and the greater patent being issued, to a further sum of 20 dol-care taken to prevent the issue of worthless lars. In the event of an appeal from the deci- patents, or the depreciation of patent property. sion of the examiners, an additional 20-dollar The regulation in this new patent act regarding fee becomes payable, as already stated. To this the use of the words, "By Letters Patent," or first cost must, in all cases, be added the patent others of similar import, affords an illustration these must necessarily vary with the drawings, with the day and year the patent was granted, agent's and attorney's fees, and the amount of of this latter fact. The word patented, together the specification, the care taken in making the must be affixed to the patented article, thus claims, the rejections of examiners, amendments giving the word patent a certain value. The of claims, appeals, &c. On the average, however, word itself is a recommendation of the article to the first cost of an American patent should not which it is attached. In this country, where the exceed one-half of that for an English patent; word patent may be attached to anything old or ever, the Trade Marks Bill now under considerand after its issue no renewal fees and no taxes new, it is utterly worthless. We hope, how. of any kind are required. ation in Parliament will remedy this evil. The clause in the new patent act which The important change made in the duration In connection with this new patent law, it is We have no doubt that the changes lately made in the American patent law, and especially the low fees and the high value of patent property in the United States, will encourage English inventors to protect their property on the other side of the Atlantic. We have dealt liberally with American inventors for many years past; they have availed themselves without hesitation of our readiness to grant patents, and, on the whole, we cannot complain of having lost anything by the encouragements we have given them. Hundreds of American inventions are patented annually in England, and we hope for the future to see hundreds of English inventions patented every year in America. For the minor improvements in the American the misconduct of patent agents, the refunding patent law-especially those regarding models, of fees in certain cases, the issue of independent patents for additional improvements, the prices of papers, patents for designs, the completing of patents within two years after the filing of the petition, &c.-we must refer our readers to the law itself, published on another page. In closing, we must not omit to state the fact that the United States' Government do not expect to derive any revenue from their patent-office. If it be self-supporting, that is all that is required of it under the American patent laws. Compare with this the conduct of our Government and Chancellors of Exchequer, who levy upon British inventors a tax of thousands of pounds annually. The contrast is not favourable to this country, and may account, to some are surpassed by American and French manuextent, for the fact that English manufacturers facturers in many departments of trade, and that our best inventions now come from abroad. We condemn, as utterly unfounded, the common ingenious, and enterprising as foreigners. The saying that Englishmen are not as inventive, sole foundation for this stigma and reproach is the fact that English genius is not encouraged. Its exercise is, in a great measure, prohibited by a heavy tax for the protection of its inventions, and by the insecurity and comparative worthlessness of English patents. LIGHTS, BUOYS, AND BEACONS. THE Commissioners appointed to inquire into the condition of Lights, Buoys, and Beacons, have issued their report; and, as it contains a great deal of valuable information, perhaps we cannot do better than give our readers the essence of the inquiry. The Commissioners were W. A. B. Hamilton, Rear-Admiral in the Navy; A. P. Ryder, Captain in the Navy; J. H. Gladstone; Duncan Dunbar, Chairman of the London Marine Board; and S. R. Graves, Chairman of the Liverpool Local Marine Board. In order to form a satisfactory opinion of the efficiency of the existing lights, buoys, lighthouses, and beacons in the United Kingdom and foreign countries, the commissioners did not summon witnesses before them for examination, but adopted the printing-press and the post. In this way more witnesses could be examined, at a much smaller cost, and their evidence, when obtained, could be more easily compared and understood when systematically collected and arranged. They say, "When a It will be seen from the above statement that the lighthouses in France are about three times as numerous, when compared with the extent of coast, as in Scotland and Ireland, and more numerous, comparatively, than they are in England. What will Mr. Roebuck, who is everlastingly boasting of his purity, poverty; and patriotism, and who imagines that no good is not a commercial country like England, it can come out of France, say to this? France has not one-third the number of ships and hibited by Professor Way, and proposed for adoption in lighthouses. Several modifications of the lime light, produced by an oxyhydrogen flame playing on a surface of prepared lime, have been exhibited in public halls, and are now proposed for use for beacon purposes; and the least powerful of these surpasses the best oil lamp in brilliancy, as the oil lamp surpasses the open coal fire. When lime lights are so perfected as to make their action certain, the optical apparatus now used will be out of date, as much as the large-turned reflector, which was first erected behind a coal fire on the Tour de Cordouan, and which was then considered a great advance in science. The object of the lighthouse-illuminating apparatus, whether constructed of glass or of metal, is to so bend the rays, which natu rally proceed in straight lines, as to prevent their waste, and to make them fall on points where they may be seen at light is thrown in any given direction. The sea. There are two powerful means whereby one is by silvered parabolic reflectors, and is "number of persons examine a witness, there is sailors that we have, but it has twice the num- called the "catoptric " system; the other is by 66 "always a tendency to depart from the special "line of examination, both in putting questions "and in giving answers, and the evidence becomes very voluminous-one subject grows out "of another. Viva voce examination is always "best for extracting the truth from the unwilling; "but written questions are best for obtaining "deliberate opinions from men anxious to give "them. A professional man could not be called "before a commission without an offer to pay "him, not only his expenses, but also for his lost "time. A great number of opinions brought to "bear on a single fact, from independent sources, "are more nearly conclusive,ifalmost unanimous, "than a small number given separately. A "number of answers to the same questions can "be more readily compared than anequal number "of answers to questions variously put in avary"ing order." The Commissioners, therefore, pre pared questions for different classes of the community. Each question was framed so as to embody but a single idea and point to a simple negative or affirmative reply; and the result has proved that many who could not leave their avocations have given their opinions and the results of their experience; and men of all ranks and professions, and of different degrees of talent, have shown that when a set of questions were placed before them they would willingly and gratuitously devote some of their time and ability to the public good. When so much public money is misappropriated in every department, it is encouraging to see a commission appointed by the Government making economy an object of attention. The commissioners were not satisfied by getting information from every available quarter, but they circumnavigated Great Britain, and visited the Channel Islands, the coasts of Ireland and France, and part of the coast of Spain. They personally inspected more than two hundred lighthouses. The following table shows the number and the nature of the lights in the United Kingdom, as taken from the Admiralty list : Total. lenses of a peculiar construction, and is called the 'dioptric" system. Sometimes the two systems are combined in one, as in the "catadioptric,"andin Mr. Stevenson's "holophotal" arrangement. ber of lighthouses, compared with the extent of coast, as England, Ireland, and Scotland. However humiliating it may be to our national pride, we cannot deny that England is behind time when so much is being done in this country France in this important particular. And at a to rival France in the arts of war, it would be The lights on shore, for which returns have equally creditable to us if we exerted a little been received, are classified in the following more energy to rival our neighbour in the wealth of nations. protection of commerce and in increasing the The commissioners say, 66 66 66 table: Authority. It will be observed, as respects number and 'position of lights, that the British coasts are not so well guarded as the French, for the lights are purposely so placed on the coasts of England "France as to cross their foe." The French have beaten us in number of lights, and shown greater skill in distributing them. The next thing which deserves consideration is the quality of light, and the commissioners have not neglected this part of the subject. They say the quality of lights depends on the following points : 1st. The character of the source of light. 2nd. The character of the apparatus by which light is directed to where it is needed. 3rd. The adaptation of the source of light and the optical apparatus to one another, with a view to the requirements of the locality. Scotland-Commis Ireland Trinity House Local sioners 8251 49 35 8 20 1 8 10 3 Apparatus. 3 11 01 01 It will be seen that the principle of refraction is generally adopted in Scotland, while that of reflection numerically preponderates in England and Ireland; but it should be borne in mind that the lighting of the Scotch coasts is of a later date than that of the English. One question put by the commissioners was, "What light have you usually seen farthest "off?" And out of the 579 witnesses, who have answered this question, the greatest distances Lundy Island, the Calf of Man, Tuskar, Flamare mentioned with reference to the lights at borough Head, Beachy Head, and Cromer, and Flamborough Head, the Lizard, Lundy, Beachy the greatest numbers of witnesses mention Head, the Start, and the South Stack, all of which are catoptric revolving lights, with the exception of the Lizard, which is catoptric fixed, and the Lundy and Start, which are dioptric revolving. The commissioners say:-" We 4th. The distinction of one light from another. Colza oil is invariably used by the general lighthouse authorities in England, Ireland, and Scotland. Where metallic reflectors alone are used, the lamp is on the Argand principle; but is resorted to. When the commissioners comwhere lenses are employed a large central lamp menced their inquiry, the Trinity House and Ballast Board used fountain lamps, and never employed more than three of the four concentric wicks. The local authorities generally employ oil lamps, but do not always use colza oil. and Newhaven use expensive sperm oil. Gas Liverpool prefers olive oil, and the Admiralty is burnt in many harbour lights, and in the beacon light at Northfleet, under the management of the Thames Conservancy. Gas is used" in the United States also with satisfactory results. are, however, of opinion that this preference of "the large reflecting lights arises, not from any "inherent superiority of the catoptric system, "but from the fact that the dioptric principle, owing to errors of adjustment, has never yet "been allowed a full and fair chance in the "United Kingdom, and a saving of oil has also "been unfortunately attempted in various ways, " chiefly by the use of the inefficient fountain lamps, in all the dioptric lights, with the exIception of those in Scotland, which has not been considered in the great revolving catop 66 " An electric light, which is produced between carbon points by the revolution of magnets fixed on wheels worked by a steam engine, has been tried with considerable promise of success by Professor Holmes at the South Foreland, and is 78 also to be tried at Dungeness or on the Start."tric lights with 30 Argand burners."-We Another electric light, produced by galvanic shall return to this subject in our next action in a stream of mercury, has been ex-number. SACRIFICIAL METALS. A CURIOUS statement made in the House of Commons, a few days ago, induces us to offer a few remarks on what may be called, appropriately enough, "the sacrificial function in metals." It was stated, our readers will remember, that the leaden envelope with which the Armstrong shell is surrounded, and which is absolutely necessary as a constituent part of that missile, might be caused to adhere securely, either by "a sort of mortise" or by the intermediation of zinc. The second expedient is that indeed adopted; with what amount of success the recent practice of these guns in China would disclose, were the Government not so pertinaciously bent on holding back the communications which have reached them on this matter. It is a fact perfectly well known to chemists, but one which mechanicians have not heeded nearly so much as it deserves, that when two metals are retained in contact, and conjointly exposed to chemical influences during long periods of time, one metal sacrifices itself to ensure the other's preservation. The history of mechanical construction furnishes rumerous illustrations of this chemical fact, as will be presently seen, when we come to cite a few examples; the marvel, then, is, that Sir William Armstrong-or, rather, the laboratory branch of the War Department, before whose cognizance the proposition of zinc soldering (thus to designate it) must have come-could ever have sanctioned an expedient which must necessarily fail in the end, like every other expedient which violates a law of nature. The history of ships' copper sheathing shall be taken as our first illustration of the sacrificial metallic function. Sir Humphry Davy, as is well known, devised a method of checking, or altogether obviating, the destruction of ships' copper sheathing. He accomplished this by attaching to the ship's bottom, at suitable intervals, slabs of the metal zinc, and which he called protectors. Protectors they were, in the following manner:-The zinc rapidly corroded, and was lost; but, so long as any zinc remained for the sea-water to act upon, the copper remained untouched. So far as copper preservation is concerned, the method adopted must be pronounced efficient. Practically, it failed, indeed, to secure the advantages described, but not for any reason that concerns us here. It was found that when copper no longer slowly dissolved, it ceased to be a poisonous metal. Barnacles and sea-weed attached themselves just as they might have done to an uncoppered wooden bottom; and, moreover, owing to a galvanic action set up, the ship's copper was rapidly fouled by a deposition of magnesia and lime, precipitated from the magnesian and calcareous soluble salts always present in sea-water. Failing, then, to achieve what was intended of it, the copper-protecting process of Davy ceased to be employed; but the failure of it is that which alone concerns us here, as illustrating what we would wish to convey by the words sacrificial metal. Take, as the next example, the illustration afforded by the setting of an iron paling-rail in a bed of lead. The most casual observation, as one passes along the streets of this city, may be made more pregnant with fact bearing upon this matter than the longest homily. For a time, varying as to length with locality, external influences, and-perhaps, in some degree -on the varying quality of the iron and lead brought into contact, both metals remain sound. But, after a time, decay inevitably sets in, and, when once commenced, marches to the issue of final destruction with wonderful rapidity. The remarkable fact is, that both metals do not decay simultaneously; it is the iron which corrodes, whilst lead-the softer metal-remains intact. Let the mechanician do what he will, this result cannot be prevented a law of nature having decreed the sacrifice, it must and will be achieved. Our next illustration shall be ordinary tin plate-iron, coated with tin, as is well known. Well, what sort of destruction is set up when tin plate has been exposed for a long duration of time to the atmosphere? Is the tin destroyed-does it tarnish even? Never. Iron is the sacrificial metal here; and, as surely as the iron is anywhere exposed, it perishes, crumbles, and dissolves away, with destructive rapidity. The rate of destruction of iron totally unprotected is slow, by comparison with that which ensues when, owing to a flaw or disintegration of the covering tin envelope, atmospheric agencies come into play upon the underlying metal. But the case we most particularly wish to direct attention to, is the result of bringing zinc into contact with iron, and retaining the two metals together over long periods, as may be seen in the so-called galvanized iron. Under this latter disposition, zinc becomes the sacrificial metal. Not one particle of iron decays, so long as atmospheric destructive agents can wreak their dissolution-so to speak-on the protective zinc. Nor does this protection alto gether depend on a complete covering of the iron. Flaws and imperfections there are, and necessarily must be, through which, quite down to the iron, destructive agents, always present in the atmosphere, must penetrate. They do not act upon the iron, nevertheless, so long as a sufficient expanse of protective zinc surface remains; and this simply because a fundamental law of nature forbids their doing so. Now, if our remarks be true and we are content to appeal to chemical science for a verdiet-what becomes of the efficiency claimed for the Armstrong shell-envelope, because of the attachment of lead by a process of zinc soldering? Sound, to the eye, these projectiles may at first seem; but a disruptive force will be acting upon them, nevertheless, from the very beginning; and in total ruin and destruction this force will eventuate at last; whatsoever Sir William Armstrong's advocates may assert, notwithstanding-whether at Elswick or at Woolwich; whether in Parliament or out of it. V being the volume, T the temperature, and P the pressure. The correctness of this formula rests upon the experiments of Dumas, regarding the density of steam at 212°, and the deductions of Gay-Lussac, who assumed that steam follows the same law of expansion and contraction as a perfectly elastic fluid. The formula is, therefore, based on theory, and up to these experiments, made by Mr. Tate and Mr. Fairbairn, its truth had not been tested by reliable direct experiments. Dr. Joule, Professor Thomson, and Professor Rankin, had announced the fact, that, for temperatures above 212°, there was a considerable deviation from the gaseous laws in the case of steam. But Mr. Tate first made experiments to ascertain exact quantitative results, and to test the precision and delicacy of the saturation-gauge, which forms the leading feature of the method on which following experiments have been conducted. em The general features of the method pursued by Messrs. Fairbairn and Tate, for ascertaining the density of steam, consist in vaporizing a known weight of water in a large glass globe, with a stem of known capacity, and devoid of air, and observing the exact temperature at which the whole of the water is just vaporized. Then, knowing the weight, volume, and temperature of the steam, its specific gravity may be calculated. Peculiar apparatus was ployed for carrying out the experiments with safety, and with the requisite amount of accuracy. The chief difficulties to be overcome, in making these experiments, were the obtaining of a uniform heat, the prevention of the globes employed from bursting, and the determination, with sufficient accuracy and delicacy, of the temperature of the steam exactly at the point when the whole of the water is vaporized. To prevent the thin glass globe from bursting, and to obtain a uniform heat, the globe was placed in a strong, closed copper steam-bath. The principle and construction of the saturation-gauge employed is very simple. It consists of a bent tube connecting two globes. A quantity of mercury is enclosed in the tube, and the whole apparatus is immersed in a large bath of liquid, to secure uniformity of temperature. Weighed portions of water are then introduced into the globes, the portions being unequal in weight; heat is applied to the liquid. bath, the water passes gradually into steam the elastic force in each globe increases in a ratio corresponding with the temperature; but the uniformity of the level of the mercury is not affected until after the whole of the water in one of the globes is evaporated, when the equality of pressure no longer exists, and the column of mercury rises in the tube which contained at first the smaller quantity of water. Fig. 1. The tem ; Thus, if 20 grains of water be in A, and 30 grains in B, and the whole apparatus be heated uniformly, until the 20 grains are converted into steam, the column A will rise. perature, noted at the instant when A begins to rise, is the maximum temperature of saturation. For reading the column levels in this saturation-gauge with rapidity and accuracy, a more convenient than the complicated French simple form of cathetometer was devised, much instrument sometimes employed for this purpose. This cathetometer is shown in Fig. 2. a is a heavy iron base resting on three levelling screws; into this is screwed firmly the planed iron stem c, and adjusted by the levelling screws in a vertical position. On the stem slides a brass block 6, carrying a small telescope t, with sight wires, and fixed by a thumb-screw behind. The stem c is graduated into inches and tenths, the block 6 and LIGHTS, BUOYS, AND BEACONS. The following table shows the proportionate number of lighthouses in England, Ireland, Scotland and France : Country. Number of : Lighthouses Coast Line. Proportion. on Shore. 1 for 14.0 Miles. Nautical Miles. England. 171 2,405 113 4,469 73 2,518 Scotland. France 1 39.5 hibited by Professor Way, and proposed for adoption in lighthouses. Several modifications of the lime light, produced by an oxyhydrogen. flame playing on a surface of prepared lime, have been exhibited in public halls, and are now proposed for use for beacon purposes; and the least powerful of these surpasses the best oil lamp in brilliancy, as the oil lamp surpasses the open coal fire. When lime lights are so perfected as to make their action certain, the optical apparatus now used will be out of date, as much as the large-turned reflector, which was first erected behind a coal fire on the Tour de Cordouan, and which was then considered a great advance in science. It will be seen from the above statement that the lighthouses in France are about three times as numerous, when compared with the The object of the lighthouse-illuminating apextent of coast, as in Scotland and Ireland, paratus, whether constructed of glass or of and more numerous, comparatively, than they metal, is to so bend the rays, which natuare in England. What will Mr. Roebuck, who rally proceed in straight lines, as to preis everlastingly boasting of his purity, poverty; vent their waste, and to make them fall and patriotism, and who imagines that no good on points where they may be seen at is not a commercial country like England, it light is thrown in any given direction. The can come out of France, say to this? France sea. There are two powerful means whereby has not one-third the number of ships and one is by silvered parabolic reflectors, and is sailors that we have, but it has twice the num-called the "catoptric" system; the other is by ber of lighthouses, compared with the extent lenses of a peculiar construction, and is called of coast, as England, Ireland, and Scotland. the " dioptric system. Sometimes the two However humiliating it may be to our national systems are combined in one, as in the "catadioptric," and in Mr. Stevenson's "holophotal " time when so much is being done in this country pride, we cannot deny that England is behind France in this important particular. And at a arrangement. THE Commissioners appointed to inquire into the condition of Lights, Buoys, and Beacons, have issued their report; and, as it contains a great deal of valuable information, perhaps we cannot do better than give our readers the essence of the inquiry. The Commissioners were W. A. B. Hamilton, Rear-Admiral in the Navy; A. P. Ryder, Captain in the Navy; J. H. Gladstone; Duncan Dunbar, Chairman of the London Marine Board; and S. R. Graves, Chairman of the Liverpool Local Marine Board. In order to form a satisfactory opinion of the efficiency of the existing lights, buoys, lighthouses, and beacons in the United Kingdom and foreign countries, the commissioners did not summon witnesses before them for examination, but adopted the printing-press and the post. In this way more witnesses could be examined, at a much smaller cost, and their evidence, when obtained, could be more easily compared and understood when systematically collected and arranged. They say, "When a "number of persons examine a witness, there is "always a tendency to depart from the special "line of examination, both in putting questions "and in giving answers, and the evidence be"of another. Viva voce examination is always "comes very voluminous-one subject grows out "best for extracting the truth from the unwilling; "but written questions are best for obtaining to rival France in the arts of war, it would be been received, are classified in the following "deliberate opinions from men anxious to give equally creditable to us if we exerted a little "them. A professional man could not be called more energy to rival our neighbour in the "before a commission without an offer to pay wealth of nations. protection of commerce and in increasing the The commissioners say, "him, not only his expenses, but also for his lost "time. A great number of opinions brought to "bear on a single fact, from independent sources, are more nearly conclusive,ifalmost unanimous, "than a small number given separately. A "number of answers to the same questions can “be more readily compared than anequal number "of answers to questions variously put in "ing order." The Commissioners, therefore, pre pared questions for different classes of the community. Each question was framed so as to embody but a single idea and point to a simple negative or affirmative reply; and the result has proved that many who could not leave their avocations have given their opinions and the results of their experience; and men of all ranks and professions, and of different degrees of talent, have shown that when a set of questions were placed before them they would willingly and gratuitously devote some of their time and ability to the public good. When so much public money is misappropriated in every department, it is encouraging to see a commis. sion appointed by the Government making economy an object of attention. It will be observed, as respects number and The next thing which deserves consideration 1st. The character of the source of light. 3rd. The adaptation of the source of light 4th. The distinction of one light from another. Colza oil is invariably used by the general lighthouse authorities in England, Ireland, and Scotland. Where metallic reflectors alone are used, the lamp is on the Argand principle; but is resorted to. When the commissioners comwhere lenses are employed a large central lamp menced their inquiry, the Trinity House and Ballast Board used fountain lamps, and never employed more than three of the four concentric wicks. The local authorities generally employ oil lamps, but do not always use colza oil. Liverpool prefers olive oil, and the Admiralty and Newhaven use expensive sperm oil. Gas is burnt in many harbour lights, and in the beacon light at Northfleet, under the management of the Thames Conservancy. Gas is used in the United States also with satisfactory results. An electric light, which is produced between carbon points by the revolution of magnets fixed on wheels worked by a steam engine, has been tried with considerable promise of success by Professor Holmes at the South Foreland, and is -Trinity Scotland-Commis House 82 51 Local. Ireland Ballast " 14 32 Board 00 51 18 6 100 100 Order of Dioptric Apparatus. 1st. 10 8 10 It will be seen that the principle of refraction is generally adopted in Scotland, while that of reflection numerically preponderates in England and Ireland; but it should be borne in mind that the lighting of the Scotch coasts is of a later date than that of the English. One question put by the commissioners was, "What light have you usually seen farthest answered this question, the greatest distances "off?" And out of the 579 witnesses, who have Lundy Island, the Calf of Man, Tuskar, Flamare mentioned with reference to the lights at borough Head, Beachy Head, and Cromer, and Flamborough Head, the Lizard, Lundy, Beachy the greatest numbers of witnesses mention Head, the Start, and the South Stack, all of which are catoptric revolving lights, with the exception of the Lizard, which is catoptric fixed, and the Lundy and Start, which are dioptric are, however, of opinion that this preference of revolving. The commissioners say :-" We the large reflecting lights arises, not from any "inherent superiority of the catoptric system, "but from the fact that the dioptric principle, « lamps, in all the dioptric lights, with the ex"ception of those in Scotland, which has not "been considered in the great revolving catop78 also to be tried at Dungeness or on the Start."tric lights with 30 Argand burners."-We Another electric light, produced by galvanic shall return to this subject in our next action in a stream of mercury, has been ex-number. SACRIFICIAL METALS. A CURIOUS statement made in the House of Commons, a few days ago, induces us to offer a few remarks on what may be called, appropriately enough, "the sacrificial function in metals." It was stated, our readers will remember, that the leaden envelope with which the Armstrong shell is surrounded, and which is absolutely necessary as a constituent part of that missile, might be caused to adhere securely, either by "a sort of mortise or by the intermediation of zinc. The second expedient is that indeed adopted; with what amount of success the recent practice of these guns in China would disclose, were the Government not so pertinaciously bent on holding back the communications which have reached them on this matter. decay simultaneously; it is the iron which Our next illustration shall be ordinary tin iron. Flaws and imperfections there are, and It is a fact perfectly well known to chemists, but one which mechanicians have not heeded nearly so much as it deserves, that when two metals are retained in contact, and conjointly But the case we most particularly wish to exposed to chemical influences during long direct attention to, is the result of bringing periods of time, one metal sacrifices itself to zinc into contact with iron, and retaining the ensure the other's preservation. The history two metals together over long periods, as may of mechanical construction furnishes rumerous be seen in the so-called galvanized iron. Under illustrations of this chemical fact, as will be this latter disposition, zinc becomes the sacripresently seen, when we come to cite a few ficial metal. Not one particle of iron decays, examples; the marvel, then, is, that Sir William so long as atmospheric destructive agents can Armstrong-or, rather, the laboratory branch wreak their dissolution-so to speak-on the of the War Department, before whose cogni- protective zinc. Nor does this protection altozance the proposition of zinc soldering (thus together depend on a complete covering of the designate it) must have come-could ever have sanctioned an expedient which must necessarily fail in the end, like every other expedient which violates a law of nature. The history of ships' copper sheathing shall be taken as our first illustration of the sacrificial metallic function. Sir Humphry Davy, as is well known, devised a method of checking, or altogether obviating, the destruction of ships' copper sheathing. He accomplished this by attaching to the ship's bottom, at suitable intervals, slabs of the metal zinc, and which he called protectors. Protectors they were, in the following manner :-The zinc rapidly corroded, and was lost; but, so long as any zinc remained for the sea-water to act upon, the copper remained untouched. So far as copper preservation is concerned, the method adopted must be pronounced efficient. Practically, it failed, indeed, to secure the advantages described, but not for any reason that concerns us here. It was found that when copper no longer slowly dissolved, it ceased to be a poisonous metal. Barnacles and sea-weed attached themselves just as they might have done to an uncoppered wooden bottom; and, moreover, owing to a galvanic action set up, the ship's copper was rapidly fouled by a deposition of magnesia and lime, precipitated from the magnesian and calcareous soluble salts always present in sea-water. Failing, then, to achieve what was intended of it, the copper-protecting process of Davy ceased to be employed; but the failure of it is that which alone concerns us here, as illustrating what we would wish to convey by the words sacrificial metal. Take, as the next example, the illustration afforded by the setting of an iron paling-rail in a bed of lead. The most casual observation, as one passes along the streets of this city, may be made more pregnant with fact bearing upon this matter than the longest homily. For a time, varying as to length with locality, external influences, and perhaps, in some degree on the varying quality of the iron and lead brought into contact, both metals remain sound. But, after a time, decay inevitably sets in, and, when once commenced, marches to the issue of final destruction with wonderful rapidity. The remarkable fact is, that both metals do not Now, if our remarks be true and we are THE DENSITY AND EXPANSION OF Ir must be known to many of our readers, the density of steam have hitherto been de- V being the volume, T the temperature, and P announced the fact, that, for temperatures above 212°, there was a considerable deviation from the gaseous laws in the case of steam. But Mr. Tate first made experiments to ascertain exact quantitative results, and to test the precision and delicacy of the saturation-gauge, which forms the leading feature of the method on which following experiments have been conducted. em The general features of the method pursued by Messrs. Fairbairn and Tate, for ascertaining the density of steam, consist in vaporizing a known weight of water in a large glass globe, with a stem of known capacity, and devoid of air, and observing the exact temperature at which the whole of the water is just vaporized. Then, knowing the weight, volume, and temperature of the steam, its specific gravity may be calculated. Peculiar apparatus was ployed for carrying out the experiments with safety, and with the requisite amount of accuracy. The chief difficulties to be overcome, in making these experiments, were the obtaining of a uniform heat, the prevention of the globes employed from bursting, and the determination, with sufficient accuracy and delicacy, of the temperature of the steam exactly at the point when the whole of the water is vaporized. To prevent the thin glass globe from bursting, and to obtain a uniform heat, the globe was placed in a strong, closed copper steam-bath. The principle and construction of the saturation-gauge employed is very simple. It consists of a bent tube connecting two globes. A quantity of mercury is enclosed in the tube, and the whole apparatus is immersed in a large bath of liquid, to secure uniformity of temperature. Weighed portions of water are then introduced into the globes, the portions being unequal in weight; heat is applied to the liquid bath, the water passes gradually into steam; the elastic force in each globe increases in a ratio corresponding with the temperature; but the uniformity of the level of the mercury is not affected until after the whole of the water in one of the globes is evaporated, when the equality of pressure no longer exists, and the column of mercury rises in the tube which contained at first the smaller quantity of water. Fig. 1. Thus, if 20 grains of water be in A, and 30 grains in B, and the whole apparatus be heated uniformly, until the 20 grains are converted into steam, the column A will rise. The temto rise, is the maximum temperature of satuperature, noted at the instant when A begins ration. For reading the column levels in this saturation-gauge with rapidity and accuracy, a more convenient than the complicated French simple form of cathetometer was devised, much instrument sometimes employed for this purpose. This cathetometer is shown in Fig. 2. a is a heavy iron base resting on three levelling screws; into this is screwed firmly the planed iron stem c, and adjusted by the levelling screws in a vertical position. On the stem slides a brass block 6, carrying a small telescope t, with sight wires, and fixed by a thumb-screw behind. duated into inches and tenths, the block 6 and The stem c is gra |