way to prevent this. It was highly important to have a good safety lamp, as otherwise many productive mines could not be worked. His recollection went back to the time when the miners were guided in their operations by the light of a steel mill-a disc of steel, worked by hand, in revolving struck a series of flints, throwing off sparks of fire. He felt they owed a debt of gratitude to Dr. Glover for his lamp, as indeed they were to any one who could enable them to work deep and dangerous mines with comparative safety. would be printed in the Journal of the Society, probably Dr. GLOVER returned thanks, and said that, with regard to the protection of the lamp from mechanical injury, he had explained that it consisted of a double cylinder, and that it would go out in an explosive atmosphere. He had not spoken at length of all the testimonials contained in the parliamentary papers, but in every test to which it had been put, the lamp had been found to answer its purposes. Mr. MARTYN ROBERTS did not see that Dr. Glover had The Secretary announced that at the meeting properly provided against any accident arising from the fracture of the glass. He regretted that he had not of Wednesday next, the 14th inst., Mr. I. J. known of the meeting in time to bring one of his own Mechi would make his "Third Report on the lamps, which he had submitted to Mr. Nicholas Wood, results of his experiments at Tiptree Hall Farm.” the coal viewer. It was composed of a double cylinder of Also that, in consequence of numerous applicaglass, the chamber between which was filled with water. Within was a trigger, attached to an extinguisher, so that tions, the Council had determined to hold an when either glass broke the water acted on the trigger extraordinary meeting, on Monday, the 19th and put out the light. With the exception of the objec- inst., at SEVEN o'clock, P.M., precisely, for the tion he had taken, he considered Dr. Glover's a most valuable lamp. of resuming the discussion "ON THE purpose The CHAIRMAN asked whether if a man attempted to attention would chiefly be directed to the diffiCONSUMPTION OF SMOKE, when it was hoped light his pipe it would put out the flame? Mr. ROBERTS replied certainly it would. culties which the furnaces employed in various Mr. BIRAM had listened with great attention to the trades and manufactures imposed to the applicaremarks of Dr. Glover. He had great pleasure in meet-tion of this plan, and how far these difficulties ing the Society, and in submitting to it a lamp of his own might be overcome. invention. His attention had been drawn to the fact that Sir Humphry Davy's lamp could not be carried through confined air with velocity without danger from the current; and also to the necessity of giving as much light as possible. He therefore reflected it through glass with the exception of a small portion in front of wire gauze, and by these means he had obtained four times the light of a Davy lamp. There was a funnel through which the air passed down the chimney, which was fastened on with a bayonet joint to make it secure; and at the top there was a perforated copper tube so that no flame could get to the air. As soon as the lamp was brought into an explosive atmosphere, the gas and oxygen would burn together, and immediately the lamp was reSIR,-Before receiving your letter, and indeed before I moved the light would go out. was aware that a paper on Mr. Berdan's machine was in An objection had been made to the lamp that it was so large that it was likely chine which, owing to some causes I need not mention, preparation, I had myself made an experiment on the mato explode; but he did not think that that objection would seemed incomplete. A partial trial had also been made in at all hold good. He should be happy to submit his the presence of some Directors of the Agua Fria Company, lamp to any test to which any other might be or had been submitted. He knew that it was capable of im-ther trial was proposed by me to be made, at the cost of the on some tailings belonging to Mr. Catherwood, and a furprovement. It was destitute of the pricker of Sir H. Agua Fria Company, for the purpose of determining with Davy's, which, however, might be easily added so as to something like accuracy the positive and relative value of enable them to lock the lamp and to make it perfectly the process. On receiving your letter, I made an arrangement with Mr. Berdan to carry out our investigation on Monday, the 28th ultimo, and the trial then made became at the same time available for the Society and the Company. secure. MR. JOHNSON had received a communication from Mr. T. Y. Hall, of Newcastle, relative to his newly invented safety lamp. The principal improvements of this lamp consisted in obtaining a better combustion with an increased light, by the admission of air at the top of the lamp, and the adaptation of an improved form of chimney. It would also cause a diminution of liability to explosion, by the adoption of gauze in combination with glass, and the use of double gauze where the air was admitted. The air was admitted by an aperture at the top, passing down between the gauze and the inner chimney or tube into a chamber, from which it was admitted to the light; or it might be admitted in the same way from the bottom. The lamp might be fed with hot oil, whereby less of it was consumed, whilst an increased light was obtained. Mr. Hall had also patented the application of the Dioptric lens to lamps of this description, by which the brilliancy of the light would be still further increased. The CHAIRMAN said, if no one had any further observations to make, he would move that a vote of thanks be given to Dr. Glover for his interesting communication. It was a subject of great interest, on which he should like to have heard a little more discussion, but, as the paper BERDAN'S GOLD MACHINE. In consequence of the difficulty of getting together, at a short notice, the Standing Committee on Mining, Quarrying, Metallurgical Operations, and Mineral Products," the Council accept, with thanks, the following Report from Professor Ansted, F.R.S., one of the members of that Committee. The experiments consisted of, 1st, the crushing and amalgamating of certain Californian ores, provided at my request, by the Directors of the Crystal Palace Company. 2nd, the crushing and amalgating certain ores from North Devon, provided also at my request by the Directors of the Poltimore Mining Company, and, 3rd, the ultimate analysis of tailings from each sample, conducted at the cost of the Agua Fria Company, by T. H. Henry, Esq., F R.S. I had also provided other samples of ore from North Wales, and some tailings resembling those already previously but partially experimented on by Mr. Catherwood. These have not yet been operated on and analysed. In order to obtain results as complete and satisfactory as possible, the machine was placed by Mr. Berdan at my absolute control, and the feeding was entrusted to two labourers, hired for the occasion, and who had never seen the machine. Owing to the latter cause some delay occurred in feeding, doubtless unfavourable to the machine. I was assisted in the investigation by Mr. Henry, who himself collected the tailings, and conveyed them to JOURNAL OF THE SOCIETY OF ARTS. his laboratory. I had also the able assistance of Mr. J. S. Atkinson, a civil engineer well acquainted with machinery, to whom I am indebted for a careful report on the power employed during the experiment, and who has assisted me also in obtaining an estimate of the probable working and general charges incidental to the use of the machine and engines required to work it. Before commencing the experiments the basins, mercury reservoir, and pit for tailings, were thoroughly cleaned out. Fresh mercury (about fifteen pounds) was put into each basin, and about 288 lbs. of mercury in the reservoir. It was observed that the gauzes through which the tailings pass away from the basins were in very indifferent condition, being partly cracked and otherwise injured. During the experiment one of them was broken off, and the fragments mixed with the amalgam. Experiment 1.-All preliminaries having been completed, the machine was started, and about half a ton (10 cwt. 1 qr. 23 lbs. nett), of very hard tough auriferous quartz, from Gold Hill, Nevada County, California (now in the possession of, and being worked by, the Agua Fria Company), was gradually supplied by hand, one half in each of the two basins of the machine.(a) UNIVERSITY CALIFORNI beams was very marked. The ore in this case was ground finer than in the former, remaining a long time mixed with the water before subsiding. The amalgam being reduced, yielded at the rate of about 1oz. 12 dwts. of gold to the ton of ore. The gold was apparently finer than the Californian, but the button was not assayed nor was its weight accurately taken. The tailings of this ore yielded at the rate of 2 dwts. fine gold to the ton of ore, the per centage of gold obtained by the machine being 93. In a former experiment it was determined, by analysis of the tailings, that the loss of mercury is extremely small. It appears likely that this loss does not exceed in weight that of the gold obtained. The machine, in its present state (although certainly admitting of some improvements), is both simple and effective, and although the basin and balls would probably require frequent replacement, it is not likely to get out of order. It requires no skilled labour, and might be entrusted to any responsible person altogether ignorant of gold working, and in this respect its advantages over any machine or process in actual use are equally certain and important. The per centage of gold obtained is decidedly very large, and from the near equality of this per centage in two ores, extremely different in nature, richness, and hardness, it would seem that the machine may be generally and safely employed on ores of average value where the yield of gold is large enough to leave a profit on the cost of working. The whole time of feeding was 1 hr. 24 min. (exclusive of a stoppage from over-feeding, owing, apparently to the want of experience of the feeders). After the feeding was concluded, the basins were kept revolving for 25 min., and there still remained a considerable quantity of sand at the close of the operation. The arrangements for removing the plug and emptying the basins occupied We have next to consider the probable charge for 49 min. During the experiment, while the mill was in working the machine. For this purpose it is fair to take full operation, the average number of revolutions of the the combination of four basins recommended by the inbasins was 19 in the minute, and the average quantity of ventor, assuming the first cost aud subsequent expenses water delivered in each basin was 10 to 11 gallons per under the least favourable circumstances. Such a comminute. On a careful estimate, the average power absorbed bination I assume to require an engine of 25 horse-power, in working the two basins appeared to be 11-835 commercial and to work continuously, except when stopped for rehorse-power, but probably nearly one-and-a-half horse-pairs or delivering the amalgam. Under these circumpower was lost by the vibration of the cross beams which stances it may fairly be considered that 16 tons of average have no bracing. In this experiment, the quartz was ex-stuff might be reduced per day by this machine in England tremely hard and tough, but was ground to a very fine powder. The amalgam being obtained from the mercury and reduced, yielded 2 oz. 11 dwts. 21 gr. of gold, whose fineness was 20 carats 34 grs., equivalent to 4oz. 4 dwts. 21 grs. fine gold to the ton of ore. On an ultimate analysis of the tailings they were found to yield at the rate of 4 dwts. 5 grs. of fine gold to the ton, the machine obtaining, therefore, 95.8 per cent. of the total amount of the gold contained in the ore. or Western Europe, at an average cost of 13s. 9d. per ton. In California the cost would hardly exceed 20s. per ton. I make no remark on this result, which will speak for itself to all those interested in gold working. I append the details, 1st, of the estimate of power absorbed during the experiment, 2nd, of the estimate of cost of working in England. Yours, &c., APPENDIX 1.-Calculation of Power. The drum on the mill, 2 basins, measured 5 ft. diameter (15 70 circumference), and made 93-6 revolutions. The strap was 6 inches, and the pressure of strap, per square foot, being 150 lbs., the area of strap, effective, was 3-5 feet. We have, therefore, 3.5 X 150 X 1469-52 (Signed) D. T. ANSTED, REPORTER. Experiment 2.-The basins being perfectly clean and To the Secretary to the Society of Arts. the mercury again placed in them, a quantity amounting to 8 cwt. 12 lbs. nett of the red oxide of iron, combined with some sulphuret, forming the gossan of the copper lodes at Poltimore, North Devon, was submitted to be crushed; one half, as before, in each basin. This ore was much less hard than the Californian, and was partly in small lumps, partly in a red, soft, muddy state. It was a portion of about one ton, forwarded expressly from the mine to my address, for the purpose of experiment. I did not observe any visible gold in any part of the ore. The time occupied by the feeding with this ore was 29 min. 30 sec. from first to last; the mill being kept going for 23 min. 30 sec. after the feeding, after which the quantity of sand was not very consider able. The removal of the amalgam occupied 1h. 23 min. During this experiment, the mean number of revolutions per minute was 19 full; the power absorbed being 12horse, as nearly as could be estimated. The water was as in the former experiment. The springing of the cross (a) This ore was part of a large quantity (about 100 tons) sent over by Mr. Catherwood about two years ago as a fair sample of Gold Hill quartz. There was barely a trace of gold visible in any part of the original cargo, and the portion employed on this occasion was selected as including the smaller specimens of ten tons, purchased a year ago for the Crystal Palace Company. These had been broken by hand, at Sydenham, to about the size of a hen's egg. 23-67 horse power, estimate. APPENDIX 2.-Estimate of Cost and Charges. Conveyance to mine, foundations and Cost of a 25 horse-power engine, complete 1250 Sundry incidental charges ... 300 £2700 150 1400 100 ON THE COTTON PRINTING PROCESS OF BY LIEUTENANT C. J. STEUART, ASSISTANT-COLLECTOR IN THE following account of the native processes of calico printing in Sindh, by mordants, by resists, and by discharges, with the materials employed, and other particulars as to the trade, is taken from a letter forwarded by the Court of Directors of the East India Company to the Commercial Association of Manchester; to whom a box, containing the patterns of printed cloths, the implements used in the process, and the various dyeing materials alluded to have also been sent. cloth passes, will give a very good idea of the implements with which the Sindhee works, and the result he produces by their means. The cloth, it will be observed, is a coarse variety of long-cloth, and is known by the natives as bafteh. The length of the nap, or floss on it (for the removal of which no means appear to be in use), is of course a great drawback to any of the minuter patterns being applied successfully to it; and thus, at the very outset, the Sindhee labours under a difficulty which nothing but the most skilful arrangement by the application of the fabric over the heated surface of an iron cylinder can, even in the hands of an English workinan, remove. The cloth is prepared for receiving the mordants in the following manner, and the composition of these, as forming the next material in use, will be given hereafter. Having been previously washed in a mixture of potash, camel's dung, and water, it is dipped in a lye, composed of oil (a), (in the proportion of one seer of oil for each piece of 20 or 25 yards to be printed), potash and water, and allowed to stand for four or five days; after which, having been throughout washed in clean water, it is placed under a heavy weight, and is then again soaked in water, and beaten out by the feet. This operation is repeated four times, and the cloth having been exposed to the sun, is dipped in a mixture made as follows:-To a quarter seer each of sakoon (b), hulleleh, and the flowers of the tamarisk, ground down to the consistency of coarse flour, as much water is added as will render the mass sufficiently liquid to soak the whole piece of cloth, which, on being saturated with it, assumes a faded yellow appearance, and is then fitted for the reception of the mordants. of procuring a variety of colours by varying the mordants It is to the imperfect knowledge possessed by the natives in use, that the poorness of their patterns may be attributed; but as in the silk-dying process, alum enters largely into best acquainted. For stamping the red colour, the prothe composition of those with which they appear to be portions are a seer of gum and a quarter seer of alum to four seers of water, to which ingredients is added as much red meth as will render the whole of the consistency of thin paste,-a consistency which is necessary in order to prevent the mordant leaving the pattern or figure which is to be stamped. The other mordant in use-which might, perhaps, with greater propriety be included under the head of colours-is made by dissolving rusty iron in is an oxidised variety of the earth known throughout Sindh by the name of "Mooltanee muttee.” The art of cotton printing, as practised among the natives of Sindh, is confined to two methods, which may be de-a liquor composed of coarse sugar and water; the gradual scribed as follows:-The first is that of printing by means fermentation of which, no doubt, produces the same effect of mordants, the principle of which appears to have been as that which is obtained elsewhere by vinegar. To ten understood in India long before it was introduced into seers of this iron-liquor are added twenty seers of water, Europe; the second, of printing by means of resists, or and the mixture is allowed to stand in an earthen pot for resist pastes, the action of which is to protect from colour- fifteen days; after which, as much of it as may be required ing matter those parts of the cloth to which they may be for immediate use is thickened with gum, and the red applied. There is also another method of printing by meth alluded to above. This latter substance takes the discharges; that is, by applying to those parts of the pat-place of pipe-clay, as is usually employed in England, and tern which are to be kept colourless, some substances which will neutralise the effects of the dye in which the fabric may be immersed hereafter; or which, by themselves combining, after the manner of mordants, with certain of the colours already imparted to the cloth, add intensity and variety to them, while they neutralise and destroy the others. It is evident that the successful application of this latter branch of the art, requires an amount of scientific and chemical knowledge which is not, as yet, possessed by the natives of Sindh, or of India generally; and the natural result is, the great want, which is apparent in all the patterns produced by them, of any but the more positive colours, and the absence of those beautiful halftints, such as pinks, olives, drabs, violets, &c., with which the English calico printer varies and adds value to the brighter dyes. A few words before proceeding to describe the process of cotton printing, as practised at Tattah, and I believe generally throughout Sindh and India, may be added regarding the materials employed, and the specimens that accompany this memorandum, together with those showing the progressive stages through which the The cloth having been prepared, as shown above, to receive the mordants, the application of these, by means of wooden blocks or stamps, forms the next portion of our subject. These stamps are generally made of the wood of the Lohero tree (Bigonia undulata), which, though sufficiently hard, yet does not possess the closeness of grain or clearness of cut which is necessary even for the coarser kinds of wood engraving. It appears to be very well adapted, however, for the purpose to which it is almost exclusively, I believe, applied by the Sindhee. Babool is also used in making the stamps; but it is found not to be quite so lasting as the Lohero. The block of wood from which the stamp is to be made, having been planed aud ground (a) Generally that made from the jhamba, or sursoon; a mixture of both is considered preferable. hulleleh, fruit of the terminalia belerica, not indigenous to Sindh, (b) Sakoon, the gall of the tamarisk, or jhow, tamarisk indica; but grows in the Deccan, koongotareh, native name for the tamarisk flowers. YELLOW.-An infusion of pomegranate bark is made by steeping a seer of this substance in hot water, to which is added a quarter seer of turmeric, and a small quantity of phitkee or alum. No gum is used, as in making the mordants. GREEN. For the green colour a little indigo is added to the abqve mixture. LIGHT RED, OR SALMON, COLOUR.-This is made of munjeet or madder root, ground to a course powder, resembling saw-dust, and mixed with water. BLUE-A weak infusion of indigo, when the whole groundwork of the pattern is to be dark blue (as in the rezaees) the same resist as is applied in the former case | having been stamped when required, the fabric is then dipped in the indigo vat All the above colours are roughly dabbed in with a bit of rag or cotton, and the operator, not been very particular as to the carefulness with which is work his done, many of the minuter portions of the pattern, such as leaves, sprigs, &c., are coloured with the rest, and have to be stamped in afterwards with blocks; these portions are occasionally pencilled in, in England, with a camel's hair brush, but I cannot find that a similar process is adopted in this country. The cloth is then boiled in water, to which a little alum has been added, and having been subjected to various washings and rinsings, each colour assumes its proper tone, and the cloth is ready for wear: see Specimen No. 5. In conclusion, a few words may be added regarding the statistics of the trade. The number of shops where this process is carried on in Tattah, is 15. Five are conducted by Mussulmans and ten by Hindoos. The number of men who find occupationin the former is 23, and in the latter 40. Women are not employed in the trade. The usual rate of payment is from four to six annas per diem, according to the ability of the workmen. The blockmakers have already been treated of. The printing of a rezace, from beginning to end, occupies about 20 days. to a level surface on a stone, with sand and water, is rubbed | is four, and they include all that are generally employed. over with a little liquid meth, in order that the pattern They are made as follows:to be marked out may be plainly distinguished on it. This is then drawn out by means of the rude pencil,— commonly a piece of charcoal-and still ruder compasses (see the specimen forwarded), and the intermediate spaces having been cleared away by the larger chisel, the finer parts are cut out with a small instrument, of which upwards of thirty are required for the various purposes of cutting, clearing, and punching holes, where it is intended that the mordant, or in other cases the colouring matter, for the stamps are used indifferently for both, should not have effect. A set of about thirty-seven blocks, the largest number employed for any one pattern, is made in a month, at a cost price of about 44 rupees, and the block engravers are generally attached to the printing establishment; there are not more than three or four men in Tattah employed on this work. To return to the blocking or printing process, this is performed by an operator who sits in front a small wooden board, raised on legs, and covered with two or three folds of cloth, or Numdah, on which is spread the bafteh prepared in the manner already described; near him are placed shallow, earthenware pans or trays, containing the mordant which has been mixed up to the consistency of thin paste, and is presented in a form suitable for transfer to the surface of the blocks by being soddened on a piece of rag immersed in the pan. This has much the same effect as the sieve which is usually employed by English calico printers, though the latter is certainly the more effectual method | of preventing the block receiving more than the thin upper coating of mordant which is necessary for the impression of the pattern. The red mordant is generally the first to be applied, and this the operator does by impressing the block which has been previously dipped into it, on the surface of the cloth, and then striking it on the back with his hand, in order to secure a perfect impression, and repeating the operation till the entire surface of the bafteh is covered with such parts of the pattern as are intended to be red. In the same manner the black mordant or colour is applied, and the cloth assumes the appearance which may be seen in specimen No. II. the red colour looks dull and dirty, and the black more nearly resembles brown or rusty purple. The cloth, covered as it is with impressions of the red and black mordants (care being taken that these be quite dry), is well washed in hot water, in which camel's dung has been infused. It is then soaked in cold water, rinsed, and at once transferred to the dyeing bath of munjeet or madder, where it is allowed to remain four or five hours. When taken out of the munjeet bath, the whole of the pattern is in confusion (ghurbar), the red colour having been suffused throughout, and it is only after being washed in water and camel's dung, and subsequently with potash and soap, the operation | gram, being repeated for five or six days, that it presents the appearance which will be seen in pattern 3. Those portions of the pattern which have received the mordants where it may be observed that the advance, which at appear bright and distinct, while the ground has lost the first is small, gradually accumulates throughout. Keepfaded yellow colour it had at first, and is now as nearly ng in mind, therefore, the rate of increase that is rewhite as it can be made in the hands of native practitioners. quired in the motion of the weight, the methods that The next operation is the application of the resist paste to have been proposed for removing the defect will now be such portions as are not intended to receive the remain- examined. These may be divided into two classes; the ing colours of the pattern. The composition of the re-first class which will be noticed was introduced by Mr. sist paste is as follows:-A seer of gum, with one seer of Eifle, to whom we are indebted for having pointed out chunan, which has been mixed with water to the thickness the defective part of the old construction and made it of cream, are dissolved in four seers of water, enough meth more generally known, although it is stated that Berbeing added to render the whole sufficiently, thick to re- thoud, Arnold, and other eminent horologists of the last main on the surface of the blocks without running. It is century, were familiar with the defect. In a work pubthen applied with the same blocks which were used for lished at the instigation of the Board of Admiralty, in imparting the mordants to those parts (in this instance 1842, several of Mr. Eiffe's plans are described; one kind red) which it is intended to protect from the action of acting upon the balance-spring, the other connected with the dyes subsequently added, powdered cow-dung being the balance. Of the plan acting upon the balance-spring, sprinkled over the surface for the purpose of drying the it will be unnecessary to say anything further than to resist paste. The cloth is now ready to receive the observe that any appendage having a variable mechanical ground colours, of which the varieties are usually very bearing upon the balance-spring will destroy the isochro limited. In the pattern before us, the number of these nous adjustment of the spring for change of arc, and ON RECENT IMPROVEMENTS IN CHRONO- BY E. T. LOSEBY. (Continued from page 38.) "With reference to the first point, it has been found by a great number of experiments and trials, extending over a period of ten years, made at the Royal Observatory, Greenwich, and elsewhere, that the law of loss of elastic force in the spring requires 1-45th of the entire compensation to increase over the effect produced by the compound lamina, in the progression shown on the diaFig. 1. where it may be observed that in addition to the ordinary compound lamina, the balance is furnished with two segments E E terminating in springs to allow of their being carried in by the lamina B. The arrangement is intended to act as follows: from the extreme cold to mean temperature the ordinary compensation is alone employed, but at mean temperature the lamina come in contact with the segments E E which are carried in from that point to the extreme heat as auxiliary weights. The effect would therefore be produced on the time during the first half of the temperature until the auxiliary was brought suddenly into action, when, as it then only moves at the same rate with the lamina, its effect would not afterwards accumulate. This class does not, consequently, fulfil the first condition, which requires that the auxiliary should gradually accumulate throughout in the progression marked on the diagram, Fig. 1. By way of familiarly illustrating this point, it may be observed that it is similar to an engine-driver, who, instead of obeying his instructions to proceed at a speed increasing at a certain rate throughout the journey, as there would be obstacles at all the stations except he arrived at the time given, should run his engine at a uniform rate during the first half of the journey, and at twice the speed during the second half, it is evident that, although he might arrive at his journey's end in proper time, he would come in contact with the obstacles at every station except the middle one. Tested by the second condition, it would perhaps be too much to say that no modification of this class could be adjusted, after long practice, without actual trial; but the extreme delicacy of adjustment, which the smallness of the motion in the lamina necessitates, renders it very improbable. The smallness of the motion also stands in the way of the class agreeing with the third condition, for as the entire motion is only 1-250th of an inch (about the thickness of ordinary letter paper), and as the points of contact between the lamina and the auxiliary would never lie further apart than half this minute quantity, it is evident) the slightest change between the bearing surfaces would prevent any action of the auxiliary at all. Concerning the fourth condition, some modifications interfere materially with the free action of the primary compensation, as in the instance before us at Fig. 2; there are, however, other arrangements, in which this condition is complied with, by having separate pieces of compound laminae for moving the auxiliary weights, and rendering them independent of the primary compensa tion. It may here be remarked that one indispensable feature has been forgotten in Mr. Eiffe's plans, viz., a banking for the segments E E to rest against during the range in which they are intended to remain out of action; for without a provision of this kind, the centrifugal force caused by the motion of the balance would keep the supplementary pieces always in contact with the rim; indeed it will be seen by holding one of these balances in a perpendicular direction up to the light, that, if the springs are weak enough for the lamina to bend them, the weight of the piece will alone be sufficient to make it fall some distance to or from the rim. This defect, however, belongs more particularly to Mr. Eiffe's plans than to the class, as Mr. Molyneux provided a banking instead of a supplemental weight being carried in; other persons have proposed arrangements which prevent a portion of the lamina bending from mean temperature to the extreme cold, the whole of the rim being free to bend in the heat, and thus producing, by opposite means, the end of making the relative effect of the compensation greater in the heat than in the cold; but besides the defects already enumerated as belonging to the class, this method, if applied to the lamina of the primary compensation, might suddenly cause a very considerable change in the chronometer's rate; for as the quantity required to be cut off from the lamina is only 1-45th of the entire length, and as the motion of the weight is only 1-250th of an inch, whilst the portion required to be taken out of action would only bend 1-45th of this quantity, it is evident the clamp could not act at all unless it embraced a much larger portion of the rim. about a quarter of an inch, so that at a few degrees below The clamp is believed to be generally made to embrace the temperature for which the adjustment was made, an error might be introduced into the compensation of a The method of cutting off a portion of the laminæ, greater amount than the supplemental error altogether. whether by clamps, arms, or springs, should therefore never be employed except in conjunction with separate pieces of lamina detached from the primary compensation, when if it did not effect much good it could not do much harm. This brings us to the second class, which, unlike the preceding, aims at producing an accumulating effect throughout, the means employed being, with one exception, different arrangements of the ordinary compound lamine. In selecting an instance from this class for examination, preference has been given to Mr. Dent's plan, as it is more generally known than any other. In the account of Mr. Dent's method, published in the fications are described, one of which is shown in "Nautical Magazine" for November, 1842, several modiFig. 3. |