"means of a watch fixed above the reservoir, which shall work "a small forcing-pump, about the size of a quill, at proper "intervals, and keep the burner always supplied; and it may "be so contrived as to stop the water while the oil is within "certain limits in height of the feeder of the burner. 66 Second, by means of a pump about 3 inches diameter and "3 inches stroke, with a light piston fixed to it, garnished with "a pliable leather, made to go easy, and perfectly oil-tight. "The stem of this piston, which guides it perpendicularly, "to be pressed down by a clock or timepiece spring in a barrel, View of Chains and Pulley. a Piston. bb Pump. c Feeding-tube. d Stem and rack. e Wheel on spring barrel. C a Piston. b Pulley. c Chain. 66 acting on the stem by a wheel and rack"teeth on the stem; but as the spring will 66 grow weaker as it unbends, and the pillar " of oil will grow heavier as the piston de"scends, to regulate these inequalities I "attach to the piston one end of two 66 66 heavyish chains, which lie over two pul"leys, at some considerable height above; "so that, as the piston descends, more weight of the chains will come to that "side, and assist it in the descent. "end (d) of the chain must be always "heavier than the other, so that it may The "Third, instead of making the piston "moveable as in the last, make it fixed; carry the feeding-pipe out of its upper 66 d a The piston fixed. c The feed-pipe. d Wheel on spring-barrel. 66 "surface; let the pump be moveable upwards by means of a spring and barrel; then, as the spring grows weaker by unwinding itself, the height of the column of oil and the weight in the pump will both grow less, in a ratio to which "it is possible to adjust a spring. 66 66 66 66 "In order to avoid too much height, the pump may be pulled up by two racks, fixed to the upper edge, and acted upon by two wheels on the axis of the spring barrel. "Fourth, last, and best. Let there be placed, about 2 inches "above the upper end of the glass cylinder, a small fly like "that of a smoke-jack, which will turn round very swiftly by "the current of air, and pretty forcibly. Let this fly have a "stem coming down in the inside of the inner cylinder; 66 perform its office by its own e Glass-holder."vis insita. The fly, indeed, will d Spindle. e Endless screw. f Crank. g Pump-rod. h Pump. Feed-pipe. " darken a small space above it, 66 "but it will serve to amuse people, and consequently will "sell if well made. In short, I like it so well, that if you "will try it, and find it answers, I will go half with you in "a patent for England, if you choose it; otherwise, it is entirely at your service to make what use of it you please. "Keir's lamp has, however, one good property which this "will not have, viz., as his pillar of saline liquor grows shorter, the pillar of oil grows shorter too. Keir's lamp may be improved in this way :-let aa be an open vessel containing oil, and bb be a close vessel containing the same "fluid, e a vessel containing air; then the oil in aa will "descend into the vessel c, by d, and the air will ascend by "the pipe e into the upper part of b, and will force the oil in 66 66 "it to ascend by the pipe ƒ as much above 6 as the surface "of oil in is below the surface in aa. By this means you "will be quit of the saline liquor and all its embarrassments, "and you may carry the burner higher than he can; and if you use a saline liquor in aa, you may carry it twice as high "as he does. Q. E. D. Sat verbum sapienti. Valeant quan"tum valere possunt, &c. &c. &c." * About a year after the date of the above letter, Mr. Watt made a pretty instrument for determining the specific gravities of liquids, having, he says, improved on a hint he had taken. "It consists of a syphon of two equal *To Mr. Argand, 8th August, 1787. 66 legs, with a tube joined to the bend of it, and a little water "in that tube. One leg being immersed in water, and the "other in the liquid to be examined, by sucking at the pipe the liquors will both rise to columns proportioned "to their specific gravities; and, if it is about 13 inches long in the legs, you can easily judge within 400 part "of the specific gravity, or, rather, of the longest column suspended." 66 So late as 1856 we have read the following announcement from St. Petersburg, showing that Mr. Watt's method is not without its followers even in the present era of more exact science :-"A very simple contrivance "has been arranged by A. Meyer, for measuring the specific gravity of solid and fluid bodies. It consists of a glass cylinder, (I presume, a precipitating glass), a glass tube in "the form of a syphon, and a brass screw vice for holding the syphon.”† 66 66 Little more than a year after the date of the specificgravity machine, he says that he had "found out a method "of making tubes of the elastic resin, without dissolving it," which recipe he offered to give to his friend the Chevalier Landriani. We have not found this method described in any subsequent letter of Mr. Watt, of which a copy has been preserved; but the subject of it was one which excited considerable interest at that time, and the importance of such tubes for a thousand purposes in science and the arts, is now universally understood. Winch and Cavallo's mode of dissolving caoutchouc in sulphuric æther, and forming tubes by dipping cylindrical clay moulds into the viscous solution, as described in works of that date, received great attention from chemists both in this country and on the Continent, as supplying a great desideratum in the apparatus of the laboratory.‡ The arithmetical machine, on which Mr. Watt says, in 1785, that he had been turning "some of his idle thoughts," he does not appear ever to have prosecuted further than by mentally considering the manner in which he could make it perform the processes of multiplication and division: pro * To Dr. Black, June 8th, 1788. + 'The Times,' 8th March, 1856. See the Travels of St. Fond,' vol. i. pp. 28-34. cesses which may be held to imply the earlier steps of addition and subtraction. But in a mind such as his, this may safely be presumed to have been already no inconsiderable stage of advancement towards the completion of such a machine. He calls the arrangement of it, as so provided for in his own view, "exceedingly simple;" but speaks modestly of "making an attempt at making it," and of it being only an attempt, from his experience of the difficulties which in mechanics intervene "between the cup and the mouth." Of the wisdom of this caution no one, probably, has been made more fully aware than that ingenious mathematician and machinist of our own time, who, at great pecuniary cost, and with still greater expenditure of ingenious thought and unwearied application, succeeded in producing a machine which realised even more than Mr. Watt's early announcement contemplated. "I have been turning some of my idle thoughts "lately upon an arithmetical machine; how I shall succeed "I know not, not having made it yet. Its properties are to "be, that when you want to multiply, you first turn up one figure of the multiplier, you then turn up in their order all "the figures of the multiplicand, and the machine will show "the product by that multiplier; you then turn up the "second figure of the multiplier, and, beginning one place "towards the left hand, you turn up again all the figures of "the multiplicand, and the machine shows the product by "these two figures ready added, and so on for any number of 66 66 figures; and it will perform division nearly as easily, with"out the least calculation or burthen to the memory, other "than to take the figures in their order, beginning at either "end you like. I intend to make an attempt at making it ;"I say an attempt, for though the machine is exceedingly simple, yet I have learnt by experience that in mechanics "many things fall out between the cup and the mouth."† Another of his contrivances, happy in its conception, and 66 It is scarcely necessary for us to do more than allude to the name of Mr. Babbage; the success of whose difficult pursuits has been so honourable, not only to himself, but also to the mechanical skill of this country, already most highly distinguished in the line of his predilection. + Mr. Watt to Mr. De Luc, 11th December, 1785. |