backs, and the march of improvement, then a very slow march, caused at length its abandonment. The frequently-recurring series of meltings required, attended as they were by expense and loss of time, was one of the most serious of these drawbacks. It is unfortunate that the names of the ingenious individuals who suggested and perfected, no doubt after much thought and experimentation, the plan which immediately succeeded the globule system, are lost in the mists of antiquity. But that plan is worthy of especial note. Cylindrical ingots were cast of considerable length and of the exact diameters of the coins to be produced; and these when cut transversely yielded, of course, discs of metal of nearly the proper thickness. The file and scales were the means of bringing them to the exact weight required, and nothing remained but to place them one by one upon an engraved die, and then administer to another die held carefully upon the piece a sharp blow with a hammer. This system is employed, we believe, at some of the Indian mints-those not under British control-up to this hour, and it cannot be denied that it is not a bad system. Indeed, with the mechanical appliances which might now be brought to bear în carrying out such an arrangement, it is by no means certain that it might not be economically and effectively carried on at home. It does not seem an irrational idea to cast bars of metal, in well-finished cylindrical moulds, -of steel or even of cast iron-of the precise diameter of each denomination of coin, and then by the rapid action of machines to cut, in the fashion of a cucumber slicer, discs of metal of the proper thickness to give each a proper weight. The melting pot would thus perform a principal part of the operation of coining, and the rolling mills would be dispensed with entirely! As it is, in most mints, rectangular bars are cast, and these have to be elongated by lamination, brought by gange to the right thickness, and then perforated by circular punches of the sizes of the various coins. Necessarily a great proportion, it is said nearly half-and it must be so-of the metal issued from the melting department must by this mode go back to it for reconversion into new bars. By the cylindrical process it is clear that a very small portion of a batch of well-cast bars would require remelting. The moulds might, in the present advanced state of mechanical science, be made as smooth within as the inside of a musket barrel, and thus perfectly "clean" castings would be obtained from them, whilst the slicing machines would at once feed the bars forward and shear them off in blanks of the thickness for florins, shillings, or any other coin, and which the stamping presses would finish most rapidly for issue. But without pursuing this digression further, we return to the history of the rise and progress of coining. screw" for the first time in the English mint. Before finally passing from this period it may be said that from the excellence of the engraving of Briot and Simon, it developed very great beauty and perfection in the coinage. Indeed, notwithstanding the more recent employment of comparatively magnificent machinery to any then in use, with elaborate arrangements, appliances of every kind, and notwithstanding the increase of salaries to officers of the Mint, amounting in the aggregate to £10,000 or £12,000, against a total then paid of £650, still scarcely an approach has since been made to the excellence of the coins they executed. When it is taken into account, also, that the inferiority of the coinage, as regards execution, is the main source of the facility of counterfeiting, and of the correlative heavy law expenses From the Red Book of the Exchequer, quoted of prosecuting offenders of the coin laws, that by Leake and referred to by Ruding, it appears becomes rather an important admission. From that the new money struck in the eighteenth year the time of Simon, the engraver, it is certain the of the reign of Edward I. was made in the follow-coinage has of the two degenerated. In the time ing manner :-First, the metal was cast from the melting-pot into long rectangular bars; these bars were cut by shears into square pieces of exact weights; then with tongs and hammer they were forged into round shape; after which they were blanched, that is, made clean and soft by annealing and boiling in acid, and then stamped or impressed by being placed as described between dies, and thus made current coin. The advantage of this change is not very apparent, for it involves a great deal of additional labour, without any proporfionate advantage. But at any rate the plan appeared to have remained in force until the year 1561. Queen Mary, however, caused an important change to be made, prior to that date-about 1546, indeed-as regarded the localities in which minting was carried on. Her popish majesty consolidated the Royal mints of the kingdom under one roof, and the provincial mints, as a matter of course, were all closed. In the Tower of London all the monies produced in her reign were coined. The year 1561 was the epoch of a remarkable improvement in the mode of manipulating money. A Frenchman then introduced the "mill and of William III. this fact was publicly announced, duction in 1810 of Boulton and Watt's powerful steam machinery, which, with sundry additions, is now employed on Tower-hill for the manipula. tion of coins, and has been heretofore described by us. It appears that from the very earliest period of the annals of coining in this country counterfeiters have successfully plied their craft; but it seems that about 1560-61 the crime was at its height. At that time a great re-coinage took place, and it is on record that of 631,950 pounds of money then re-coined only 244,416 pounds of "fine monies" could be produced, whilst the dross of this mass of metals was "carried to foul highways" and places where rubbish might be shot. In fact, the bulk of waste in this re-coinage must have been considerable, as the difference of weight after the metal had been reduced to standard was 387,534 pounds. A strange story is told, too, of the workmen engaged in melting down the base coins; "most of them," it is said, "fell sick to death with the savour, and were advised to drink in a dead man's skull for their cure, and, accordingly, a warrant was procured from the Council to take off the heads from London-bridge and to make cups of them, out of which they drunk and found some relief, (?) although most of them died." It is probable that the sickness arose from their inhalation of the fumes of arsenic with which the base metal was mixed, but it is very questionable whether the medical prescription was a good one. There are other interesting particulars in connection with the progress of minting, and it is not unlikely that at an early opportunity we may recur to the subject. STEAM SHIP ECONOMY. of the paper presented by me to the British As- In 1662 Blondeau triumphed over the banded opposition which had caused his disappearance from the country, and agreements were entered into with him to "furnish all the mills, rollers, presses, &c., &c., necessary, and to instruct the moneyers in the use of his newly-invented tools and engines." The moneyers were bound to pass the plates of gold or silver through the horse mill, and to cut, flatten, size, neale, blanch, and coin the pieces; to maintain the horses, to find alum, argot, and sawdust, to keep in repair the ovens, furnaces, and utensils for nealing and blanching; to make good the balances, small files, tubs, trays, bowls, and sacks, and all waste of gold and silver in nealing, blanching, and working. This was, therefore, the horse stage in the history of the coinage. With certain modifications of ship comes to be compared with that of a standard details the principles of Blondeau's plans of coin-type; under such a system of comparison one ing were successfully acted upon until the intro- I ship with another, it may be expected that steam Woolwich. BY CHARLES ATHERTON, Chief Engineer, Royal Dockyard, Public usefulness, as dependent upon science, being the great object for which the "British Association for the Advancement of Science" was originated, and has now been signally upheld for 29 years, a period remarkable for the progress that has been made in the utilisation of the powers of nature to such extent that the international condition of the globe is now being revolutionised by the progressive practical utilisation of elements which heretofore were regarded merely as phenomena of nature, viz., steam and electricity; in which revolution the application of steam to the purposes of navigation has played so conspicuous a part, that now, in proportion as steam may be effectively employed in the pursuits of commerce and of war, it is acknowledged that even nations will rise and fall. | period in the history of steam navigation has so great a step been made in its practical development as may now be said to have been realized by the fearless introduction, in marine engineering, of the long-known and well-understood effects of increased pressure, superheating, and expansion; the recognition and application of which principles has now, at length, been attended with such effect in marine engineering, that the consumption of fuel with reference to power is now shown to be practically reduceable to less than one-half of the ordinary consumption on board ship. ing, also, that mercantile enterprise, setting no Seeing limits to speculative investments, has in these days emancipated mechanical intellect from the fetters by which ideas as respects magnitude have hitherto been bound. Under such circumstances I cannot doubt that any effort to popularise a knowledge of the practical utilisation of steam, with reference to the consumption of fuel, though advanced with no pretensions to science, beyond that which may be awarded to originality and labour in the application of calculations to develop ing useful results, will be favourably received; more especially as the paper which I now beg to present is in continuation and conclusion of an inquiry which has already, in part, on two occations, been favourably entertained by this Associa sion, and honoured with a place in its published records. Seeing, moreover, that at no The former papers to which I allude are:-1st. "Mercantile Steam Transport Economy with reference to Speed."-Vol. for 1856. p. 423. 2nd. "Mercantile Steam Transport Economy, with reference to the Magnitude of Ships, and their Proportions of Build."-Vol. for 1857, p. 112. And I now purpose to bring this inquiry to its conclusion by the following paper on Mercantile Steam Transport Economy, as affected by the Consumption of Coals. My purpose, and the drift of my remarks, will, probably, be the more readily understood by my at once adducing the following tables C and D, and the diagram E, in continuation of the tables A and B, which are published in the Volume of Transactions for the year 1857, pp. 116 and 119, observing with reference to these tables C and D, that the rate of consumption of coal on which the calculations are based, viz., 24lbs. per indicated horse power per hour has been practically realised on continuous sea-service, although the ordinary consumption of steam-ships in the Royal Navy, as well as in the best vessels of the most celebrated steam shipping companies, is, I believe, at the present time, fully 50 per cent. in excess of that amount; and I may say, that in steam ships generally, the consumption of coals per knot of distance, with reference to displacement and speed, is double the consumption which these tables, based as they are on an example of existing practice, show to be now practically realisable. The tables now adduced are as follows:Table C, calculated for the speed of 10 knots per hour, showing the mutual relations of displacement, power, and the consumption of coals per day, per hour, and per knot, for vessels of a gradation of sizes, from 250 tons displacement up to 25,000 tons, the co-efficient of dynamic perforV3 D mance, deduced from the formula being ind.h.p. assumed to be 250, and the consumption of coals being assumed to be at the rate of 24 lbs. per indicated h. p. per hour. On these data, the coefficient with reference to coals deduced from the formula (0 being the consumption of 10 coals per hour expressed in cwts.) becomes 11,210. Table D, showing the mutual relation of displacement, power, and coals consumed per day, per hour, and per knot, for the respective speeds of 10, 15, 20, and 25 knots per hour. The data on which this table is calculated being the same as above described for Table C. Diagram E, showing approximately by scale the nautical mileage consumption of coals for vessels from 1,000 tons displacement up to 25,000 tons, deduced from Table D. It will be observed that in Table C the tabulated sizes of ships, as determined by their respective load displacements, increase progressively from 250 tons displacement up to 25,000 tons, showing under assumed conditions, which, however, are justified by the present circumstances of realised advancement in steam navigation, the mutual relations of displacement and coals calculated for the speed of 10 knots per hour as most convenient for a standard of reference. The in TABLE D. Showing the Mutual Relations of Displacement, Power, and Coals consumed per Day, per Hour, and per Knot, for the respective Speeds of 10, 15, 20, and 25 Knots per Hour. The Co-efficient of Dynamic Performance being deduced Displacement in V3 Dr ind. h.p. being assumed to be 250, and the Consumption of Coals being assumed to be at the rate of 2 lbs. per indicated horse power per hour. Tons weight, at 35 cubic ft.of Sea Water per Ton. Tons. Cwt. 250 52 159 4.26 3.55 ⚫36 300 59 179 Per Knot. Ind. H. P. Per Knot. Per Knot. Ind. H. P. Per Knot. 1,350 36-1 30.1 2.0 3,200 85.7 71.4 3.57 6,250 167 139 5-56 40.8 34.0 2.27 45.2 37.7 2.51 3,614 4,005 107 96.8 4.03 80.7 7,058 188 137 6.28 89.4 4:47 7,822 210 175 7:00 Diagram showing approximately the Nautical Mileage Consumption of Fuel, for Vessels from 1,000 tons displacement, up to 25,000 tons, the Co-efficients of Dynamic Performance deduced from the Formula VD being assumed to be 250, and the Consumption of Coals being assumed to be at the rate of 23 lbs. per Ind. H. P. per hour. Having thus explained the use and application of Tables C and D and the Diagram E, it will be perceived that the task which I have undertaken on this occasion is to show palpably by comparison with these tabular statements, based on data within the limits of already realised results, taken as a standard, what is the character of steam-ships as respects their locomotive or dynamic capabilities, with reference to the economic performance of mercantile transport service, so far as dependent on the consumption of fuel, thus affording an exposition whereby parties interested in steam shipping, either as owners or directors, or agents, or as the charterers of shipping for Government or for private service, though unacquainted with the details of marine engineering as a science, may be Again, let it be supposed enabled to arrive at some definite appreciation of that the weight of the hull the amount of work that may be expected of of a ship of 5,000 tons steamers; that is, the weight of cargo they will displacement fitted for carry, and the length of passage capable of being sea amounts to 40 per performed at any definite speed, for, as before cent. of the displacement, observed, the dead weight of cargo that a ship or 2,000 tons, and sup- will carry is equal to the tons' weight of water pose the weight of the displaced between the light and load waterand boilers to lines of the ship, less the weight of coals rebe one ton for each 10 quired for the voyage, and which for long indicated h. p., the vessel voyages commonly amounts to four times the requiring, as shown by weight of cargo chargeable as freight, and it Table D, 1,170 indicated constitutes the limitation of distance which the h. p., to attain the speed ship is able to run under steam at a given speed. of 10 knots per hour, with This inquiry is therefore essential to a due apa consumption of coals at preciation of the economic consequences which the rate of 2.61 cwts. per are involved in progressive variations of steamknot, then on these data, ship speed, especially as respects the high rates of the engines, to attain the speed, which are occasionally professed, but which speed of 10 knots per are seldom realised, simply because there has been hour, would weigh 117 no recognised exposition whereby such preten. tons, and the weight of sions may be judged of with reference to the coals for a passage of, required consumption of fuel. In short, regarding say 12,000 nautical miles, this matter as a public cause, affecting as it does would be 12,000 x 2:61= the pecuniary interest of the public to the extent 31,320 cwts., or 1,566 of millions sterling per annum, my object is to tons weight, making promulgate, through the medium of the together for hull, en- notoriety which every inquiry obtains upon its gines, and coals, 2,000+ being brought before the notice of the 117+1,566-3,683, and «British Association for the Advancement consequently the displace- of Science," a Mercantile Steam-Ship Exment available for cargo positor, by reference to which as a standard of 1,317 tons weight. But if comparison the good or bad qualities of steam shipping may be determined; and this surely is a public cause, for by the operation of the scrutiny which such a system of comparative exposition may be expected to inaugurate and popularise, steamers will soon become marketable, with reference, in great measure, to their capabili ties for economic transport service, according to the speed that may be required; and under the influence of this scrutiny all bad types of form and vicious adaptation of mechanical system, will be eradicated; incompetency in steam-ship management will become gradually eliminated, and the mercantile transport service of the country being then performed exclusively by good, well-appointed, and well-managed ships, would be performed at a minimum of cost to the shipping interests, and consequently to the best advantage for the interests of the public. Hitherto the dynamic character of steam-ships has been a mechanical problem enveloped in undefined and even delusive terms of shipping and engineering art; consequently, its determination has not been based on any recognised principles of calculation. Hence the dynamical character of shipping has been a mystery-a matter of mere assertion on the one hand, and of credulity on the other. But mystery being unveiled, commercial vision will be opened, and competition, in shipping as in any other well-understood and open field of public enterprise, will insure the mercantile ransport service of the country being performed To the best advantage, and it will gradually establish and preserve the just equilibrium of trade as between the carriers and consumers of all the sea-borne productions of the earth. A SAFE and efficient apparatus to enable operations to be conducted under water has long been considered a very important and desirable object. of attainment. Mr. Heinke, who is well known as an engineer who has spent the best part of his time of late years in submarine operations, has recently patented a new apparatus which combines so many improvements that we have much pleasure in introducing it to our readers. It consists of a diving helmet, which is attached to a waterproof dress, and a submarine lamp, which forms a most useful adjunct. We will first describe the helmet. Upon the breast-plate of this helmet, and in front of the diver, is placed a safety valve, so as to be easy of access, which at any moment he can close partially or wholly, so as to regulate the egress of the air fed down from above. If he shuts this valve completely, his waterproof dress is at once inflated, and his buoyancy becomes so great that without any effort he rises to the surface like a cork, in a much more expeditious manner than he could climb up by the ladder, or even be drawn up by those stationed above. If at any time part of his dress should become injured, or the glasses before his eyes be broken, the opening thus formed can in an instant (by closing the valve) be turned into the egress hole, and the air made to take that course, to the total exclusion of the water. The value of this improvement has been well exemplified in the course of the work upon the new Westminster Bridge, where Heinke's apparatus is exclusively used; for in one instance a diver struck one of his glasses against a spike, and if he had not closed his valve, water would instantly have been admitted, and, doubtless, he would have been drowned; but, as it was, he turned the valve, and felt no inconvenience, nor were his clothes even moistened by the accident. We subjoin a woodcut showing a section and ele vation of one of Heinke's helmets, as also a sectional view of the valve. Fig. 1 shows a front elevation of the helmet itself. It will be seen from this that the openings are also provided (as an extra safety-guard) with segmental plates, so that by turning either disc round by means of the buttons which project from the circumference, the openings can be closed instantaneously. The regulating or safety valve is seen in front of the helmet, just below the joint indicated by the letter A, which joint enables the whole top of the helmet to be taken off at pleasure. Fig. 2 shows a section through the head-piece, exhibiting the pipe at the back through which the air is fed down the valve for safety in the event of the bursting of a feed-pipe. From the orifice will be seen the tubes, extending over the upper internal surface of the helmet, for leading the stream of air over the glasses; and again below, and marked by the letter B, will be seen the safety valve beforementioned, which can be opened or shut at pleasure by the diver. This valve is shown in section on a larger scale in Fig. 3. It will there be seen that an ordinary valve, which is held in place upon its seat by means of a spiral spring, is covered with a cap perforated on the top, so as to allow of the escape of such air as passes, but so fitted as to turn upon the outside of the valvebox or seat at pleasure; this is provided with a long slotted hole, which runs some distance around its circumference, and the lower part of the valveseat or box is provided with a similar slot. From this description it will be apparent that the cap can be turned so as either to let the two holes be in one, and thus open to allow of the escape of the air, or be closed, should it be desired; by this simple contrivance the diver can regulate the egress of the air, and so the extent of the supply to the greatest nicety. We must now pass on to the latest of Mr. Heinke's improvements, that of his lamp. Figs. 4 and 5 show a side elevation and longitudinal section of this lamp, which, it will be noticed, possesses the following peculiarities and advantages. The amount of air which is supplied through the pipe 4, Fig. 4, can be regulated by means of the tap; the air thus admitted flows into the external ring or case, which is shown by the letters B B in the sectional elevation, Fig. 5; it then finds its way through the perforated plate C C, at the bottom of the ring, into the receptacle D D, and thence through the strainer E into the lamp itself, for the support of combustion. The burner itself is of the form commonly called argand, and supplied with oil or gas fro u the ring F, which is made open, so as to allow of the light from the lamp being thrown down, from the reflector G, through the lense H, so that by this means the bottom surface of the sea can be examined without removing the lamp from its upright position. The lamp is also provided with two side lenses I I; or three can be used if re quired. The upper cap is fitted with an internal cone, which is connected with a pipe leading to the surface of the water for the escape of the products of combustion. This lamp gives a brilliant light, and the air supplied percolating through the lower ring enables it to burn steadily, a matter of considerable importance in such cases. We have now described in detail an apparatus by means of which a man may in comparative safety proceed to his labour at the bottom of the sen Emigrant ships, and in fact all others, but more particularly screw vessels, if furnished with an apparatus of this sort, would be provided with the means of investigating the causes of leak, &c., and, in many instances, of counteracting their fatal effects without the waste of time which would arise from returning to port. Possessing as Mr. Heinke's apparatus does so many advantages, it is not to be wondered that it is becoming every day more extensively used. The readers of the Times will have noticed that it has been employed upon many large works, and, amongst others, in removing the foundations of the old bridge at Rochester; in this instance some of the officers of the Royal Engineers were persuaded to descend in one of the dresses, and they did not, they tell us, experience any unpleasant effects. THE GREAT EASTERN EXPLOSION. OUR readers will have observed that we have steadfastly refused to discuss the so-called scientific evidence given at the Weymouth inquest, our reason being that the newspaper reports of that evidence (which are the only ones accessible to us) differed so considerably as to be altogether unreliable. A scientific contemporary, the Engineer, regardless apparently of this consideration, took an opposite course, and published certain severe strictures upon some of the gentlemen who were examined. Among others Mr. Galloway, the Board of Trade Surveyor, was visited with criticism of a somewhat unsparing character. This has naturally enough given great offence, and has awakened in some professional gentlemen a desire to rebut the allegations and refute the arguments of our contemporary. For this purpose they have addressed a letter to us, alleging that so much unfairness and hostility to Mr. Galloway is evinced in the article of which they complain that they will not put themselves into communication with the editor who is responsible for it, and requesting us to publish their rejoinder. Now, to pacific persons like ourselves, such a proposal cannot possibly prove altogether pleasant, because the simple insertion of the letter of our correspondents may, for aught we know, be presumed to constitute an act of hostility to our contemporary, with whom we have not the slightest desire to wage war. But, on the other hand, since the reputation of a public officer has been attacked by him, and since we ourselves believe the attack to have been made too warmly (although not, we firmly believe, with any personal or vicious intention), we see no sufficient reason why we should refuse to aid in the vindication of the right. But then, again, our correspondents have written a very fierce letter, and have reciprocated the spirit of their antagonist very hotly, and we object to everything like heat or fierceness in what we publish; thus a new difficulty is created. Well, there is, happily, the good old golden rule to guide us even in this strait, and by its aid we may perhaps succeed in doing justice without giving offence. We will, therefore, do by our contemporary as we should wish him to do by us, by publishing our correspondents' statements as free as possible from what s splenetic or personal. If this course should ive offence to either party we shall hold ourselves anocent of it, and arm ourselves for the conse quences. As we dare not, of course, amend, but must simply omit portions of the following letter, we shall not attempt to bring it into a form in which we can wholly approve it. Some things will probably remain which we should prefer to see omitted, but which the necessities of the case require to stand. Intrinsically, however, the communication will be found of a most valuable cha racter. In order to aid the reader in understanding the question, we have had engraved the accompanying illustration, showing the arrangement of all the cocks at the moment of the explosion. With these explanations we produce the letter, which (when pruned) runs as follows:TO THE EDITORS OF THE "MECHANICS' MAGAZINE." October 1st, 1859. GENTLEMEN,-With the recent catastrophe on board the Great Eastern, the readers of our mechanical and other journals have been regaled these last few weeks almost to surfeiting, and in connection with this sad event has the propensity to mislead been singularly manifest, not only by much of the evidence given at the inquest, but by many of the various letters, comments, leading articles, and other effusions which have from time to time been introduced to public notice. Nor would we trespass on your valuable space but for a desire to correct several glaring errors to which the pen of a contemporary of yours, whose pages are devoted chiefly to the discussion of mechanical matters, has given publicity. In an article in the Engineer, headed "The Great Eastern," a most unaccountable attack has been made on one of the witnesses who gave evidence at the inquest at Portland, and as the grounds of those charges are as absurd as they are at variance with truth, we beg your patient indulgence while we attempt to set the public right on points on which (thanks to the article we refer to, and others of a kindred character) they are grossly misinformed, and let us state at the outset that we shall speak of what we saw and know from facts, and not from any second-hand reports of the character contributed by "our correspondent, a practical engineer." The first indication of that disregard for truth which appears to characterise the writer of that |