Chap. 9.]

Explosive Engines.

471

and other mills; and he thinks in the hot months, at least, a steam-enginemight be made to raise by the sun’s heat water enough from a well to.replenish fish ponds &c, as opportunity served. We have long thoughtthat solar heat will yet supersede artificial fires to a limited extent in raisingsteam, as well as in numerous other operations in the arts, especially inplaces where fuel is scarce. It is a more legitimate object of researchthan one half of the new projects daily brought forward.

The mode adopted by Watt for supplying water to his boilers by meansof a float attached to a iever, and so arranged as to open and close a valvein an adjoining cistern, was not invented by him. lt was employed byMr. Triewald, the Swedish engineer , in 1745, in his apparatus for commu-nicating heat to green-houses by steam, and is described, with a figure, inthe London Magazine for 1755, p. 18—21.

Hearing green-houses by steam is mentioned by an English writer in1660. Rivius, in 1548, speaks of eolipiles being employed to impart anagreeable temperature to apartments in dwellings. Col. Wm. Cook’s“ Method to warm rooms by the steam of boiling water,” is described,with a cut, in the Gentleman’s Magazine for 1747, p. 171. A boiler wasto be heated by the kitchen fire, and the steam pipe to ascend through onetier of rooms, and descend through another, traversing backwards andforwards in each room according to the temperature required ; the escapeof the Condensed and waste steam being regulated by a cock.

A patent for cooking by steam was taken out in England by Mr. How-ard in 1793. He named his apparatus “a pneumatic kitchen.” Repertoryof Arts, vol. x, 147.

There are two other classes of motive machines that we intended hereto notice in some detail; but as they have not come into general use, andthis volume having already nearly reached its prescribed limits, a briefsketch may suffice. The origin of most of them may be traced to attemptsto supersede steam by more portable fluids, or such as require less fuel togenerate. We allude to explosive and to vapor engines. Of all the devicesto which the steam-engine has given birth, none possess greater interestthan these. Some were designed to raise water directly, and all of themindirectly. The first dass are named from the force by which they actbeing developed by the firing (generally under pistons) of explosive Com-pounds. These are either concrete or aeriform substances, as gunpowder,a mixture of hydrogen gas and common air, &c. Those of the seconddass are similar to steam-engines, except that they are worked by elasticfluids evolved from volatile liquids, or such as pass easily and at low tem-peratures into the aeriform state, as alcohol, ether, &c.

Explosive like steam engines have been made to act in two differentways, according to two opposite properties or effects of the exploded sub-stance—the expansive force developed, and the vacuum or partial vacuumwhich succeeds. For the purpose of explanation, suppose two large re-peating guns or muskets, provided with small charges of powder only, tobe secured by a frame in a perpendicular position, with their muzzles up-wards, and three or four feet apart. Directly over them let there beadapted a working beam, somewhat as in the last figure, suspended on afulcrum at an equal distance from each. Suppose the ramrods placed inthe barreis with their buttons or plugs so made as to fill the bore, andwork air-tight like the piston of a syringe or pump. Let the upper endsof these rods then be connected by a bolt to the ends of the beam, whichshould be at such a distance above the muzzles that when the plug of onerod is at the bottom of its barrel, that of the other may be just within the