The [third figure] of [Plate 26], offers an end view of this cage or frame, shewing the expanding vessel at B C A D, where the strengthening ribs of [fig. 2] are seen endwise at 1, 3, 5, 7, &c. and moreover, F G and H are the pillars or cross bars by which the parallelism of the two end plates is effected and secured.
There remains an important subject to be considered: How to make the corner joints D C, and the end joints steam or water-tight as required. The small [figure 4] answers the question as far as water is concerned. A is a strip of leather screwed more or less near to the edges of two contiguous sides of the vessel, so as to cover the joint or hinge, and make it water tight whether the pressure come from within or without. This figure also shews the grooves which receive the stuffing to close the ends of the vessel, by sliding against the plates or cheeks E F, &c. [fig. 2]. The several members of the corner joints themselves should be well fitted into each other: so indeed as almost to close the vessel without any stuffing. Nor need we in all cases be anxious about this stuffing; for I think it very possible to make this joint close enough for pumping or blowing without any such provision. I observe, however, that the leather A, [fig. 4], might give place to a strip of thin metal, bent into the same form, (or nearly so) the elasticity of which would leave play enough for the joints, on the supposition of working only with a moderate degree of motion in the said joints.
I should not have given this idea so much attention, had I merely wished to use it where the cylinder-motion now applies: But my present views go further. I foresee the use of this Machine for very low pressures—and in very large dimensions; and I can conceive a proportion between it’s length and height, that shall as it were annul the effects of friction and leakage, compared with those of the cylinder-formed piston. But I do not undertake, or hardly wish now, to exhaust this subject: being more anxious to deliver the idea to my readers, than to announce all I intend to undertake by it’s means. I shall, therefore, merely finish the description of the other [figures 5] and [6] of this [Plate]. The first, is a small hand pump on this principle, having a suction pipe A, and a rising pipe B, both having proper valves and opening into the expanding vessel, as worked by the handle C, much in the manner of a common pump. It will therefore act by it’s expansive and contractile properties; and have one good quality we should seek in vain elsewhere—It will begin the motion of the water with a softness unknown in the use of pumps in general.
In fine, the [sixth figure] shews a System of this kind applied to the two objects, of giving power, and using it. The vessel A B, receives the power from steam or any other agent; and the vessel C blows a fire, raises water, or does any analogous work, without requiring any other parts than those here displayed.