In this calculation, I have not forgotten that the vertical and horizontal motions are nearer alike, when the bars are not drawn so tight at K H; that is, when the joint I is lowered. But it is equally true that, when the joint I rises still more, the difference between these motions is still greater; so that, as a medium effect, I think we may reckon on an eight-inch stroke in the present case.
The question now recurs, of what strength are these strokes? Are they sufficiently powerful to produce a useful effect with so short a motion? This I cannot say from experience; but, from the known strength of iron and steel, their power, in these dimensions, must be very great. A few more observations may occur in the course of the enlarged description we shall give of the Machine itself.
A B C are three pipes of cast iron, well turned at the end, and having conical points of iron, well steeled, let into them, so as to have no tendency to bend. a b c are three steel bars, placed in troughs, so as to be heated or cooled by water poured into the latter. Or, these troughs may be exchanged for tubes, to admit heated or cooled air, according to the means used to cause these mutations. In a word, although I have represented these bars as contained in troughs, I intend to finish my description, on the supposition that they are tubes, because I intend to suppose the Machine worked by air instead of water.
To proceed: at d is an opening under the tube B, into which air enters, and C is an opening on the top of the tube which emits the same air, the three pipes being made to communicate by means of a short junction-pipe at each of the angles D and G. Here, then, the fire-place f g, [fig. 2], must be noticed: the use of which is both to heat and cool the Machine; and the following are the means:—This little instrument contains fire in it’s middle compartment, and that fire draws air into the part f, and drives it out of the part g. It also turns on a centre-pin, seen in the [figure]. This chaffing-dish, then, is placed at i d, and there serves a double purpose. When it’s pipe g conveys heated air into the pipes B A C (and out at C), it heats those pipes and expands them; but, at the same time, the pipe f of this instrument draws cold air through the three tubes a b c, in which are the steel bars that require to be contracted: both which operations conduce alike to the above-described effect. By these means, the weight w is raised, and (for example) water sucked into the pump X. But, turning the fire-place half round, we reverse this effect. The hot air is now drawn, out of the pipes A B C, and cold air drawn through them, by which they are cooled; while the hot air, from the fire, is thrown through the pipe g into the tubes a b c, and passing through the chimneys k l, there heat the bars and expand them,—both which operations concur in letting down the weight E, and thus, in forcing the water of the pump to whatever destination was previously assigned it.
OF
A MACHINE,
For Making Laces, Covering Whips, &c.
Many people, in these parts, have seen a certain machine, said to have been invented by an inmate of that laudable institution the Liverpool Asylum for Blind People; for the purpose of making laces, covering whips, &c. I hope the similarity of name will not induce any reader to suppose that I have had that machine in view, and am endeavouring to cast it into the shade, or purposely to supersede it. If any person should thus think, I have a safe reply at hand. My own invention (somewhat less perfect than it now is) was made, many years ago, on purpose to serve an Asylum for the Blind in Paris!—a reflection with which I shall, at once, close this, perhaps, unnecessary apology.