196

ALLEN'S FURNACE.

expensive evil, he ascertained, that water evapo. rates after the rate of an inch and a half in depth per hour; from which he drew the conclusion, that the larger the surface of boiler exposed to the action of the flame, the greater would be the evaporation or production of steam. He, therefore, placed his fire in the centre of the boiler, and by this means it was surrounded by the water which was to be heated. His furnace was of copper, brass, or iron, of a peculiar form or feature, (similar to that used in modern steam-boats,) and the water was contained in the space round it by a vessel of wood, lead, or any other material that would hold water.*-This was his first scheme. The second is similar, with this difference only, that, as he had observed, in common cases, the flame rise above the chimney-top, after encircling the boiler once, he made his smoke-flue with numerous cork-screw-like windings through the water, in the manner of the worm of a still; lest the length of the passage should extract all the heat from the smoke, and thus act as a

"The mode of conveying flame through water had been practised by others before my time, (1770,) and was common in the Cornish mines. The inventor is unknown, but a person of the name of Swaine was a great propagator of the practice.-Watt, in Robison's Mechanical Philosophy, vol. ii. This was probably Allen's mode; but it was also known before his time. Sir Robert Moray and Dr. Goddard, in 1663, proposed brewing beer in a kettle, having only a brass bottom; and in the middle thereof, a globe of brass open at the lower end, into which the fire goes, whereby the brass of the rest of the kettle is saved. Glauber used wooden casks for boilers, but he boiled the water they contained by a small copper globe, (a pipe from which was inserted into them,) placed in a furnace heated with sea-coal,"-" a contrivance," says Hooke, when describing it, "which, if prosecuted, might be perhaps very beneficial to brewers, dyers, and such other trades as have occasion to make use of great quantities of water heated."

ALLEN'S STEAM-BOAT.

197

❝ damper on the fire-place; he recommended the employment of a large pair of bellows for forcing the sluggish vapour into activity.

Meritorious as these schemes must be thought, considering the period at which they were proposed, it does not appear that much benefit could arise from their adoption, with the exception of the saving of the heat which was absorbed by the fire-place; and probably, also, of that portion which was lost by radiation from the surface of the boiler when formed, as was usual, with copper or iron-for the wooden boiler could not radiate much. The doctor made no attempt to ignite the gaseous product of the coal before it passed into the "tunnel." This was left to find its way as before, merely "cooled a little," into the atmosphere.

The explanation of these schemes, and a discussion of their advantages, occupy the first chapter of the Doctor's treatise. The second is devoted to an account of an invention of a more imposing character a mode of navagating a ship in a calm.

Other projects for propelling a ship in a more expeditious and less laborious way than by oars, which had been proposed by others, he enumerates, before entering upon the merits of his own. "In these," he says," the motion was communicated by machinery, working without the ship, something analogous to oars or paddles, or by the revolution of wheels turned by a capstan placed within the ship." No part of his machinery, on the contrary, was placed on the outside of the vessel.*

*He quotes an experiment made by a French author on the gallies in the Mediterranean. "A fifty-two-oared galley, the oars thirty-six feet long, with three men to each, moves

198

EXPERIMENT ON CANAL.

The way he proposed to get a power and avoid the defect, which attached to every method that had been practised or proposed, was to form a tunnel or pipe open at the stern or hinder part of the vessel; and by means of a pump to force water or air into it through the sea, and by the reaction which this would occasion, the ship would be driven forward, very accurately "imitating what the author of nature has shown us in the swimming of fishes, who proceed in their progressive motion, not by any vibration of their fins as oars, but by protrusion with their tails; and water-fowls swim forward by paddling with their feet behind their bodies."*

The doctor carried his scheme into practice, in a boat of considerable size upon a canal; and from that and other experiments, he felt certain, that the protrusion of something at the stern was the true way to navigate a vessel.-But his scheme is detailed here, on account of his suggestion, that the operation of pumping, which was performed by men in his trials, could be better accomplished by the power of a steam-engine, "and he could have no manner of doubt that, if a couple of them were applied to a ship of four

at the rate of three miles and three-quarters an hour.-This effect is equal to a force of fourteen pounds exerted by each rower; the cross section was equal to eighty square feet.".

"It may be remarked, that, at a very early period, aquatic automata, furnished with wheels and other similar contrivances, were moved by other means besides those derived from animal power. Roger Bacon, de Admirabili Potentia artis et naturæ-and J. C. Scaliger, exercit. 326, ad Cardanum.-Babington's Pyrotechnia, cap. 60.

"In 1732, The Comte de Saxe revived the project of wheelboats, and presented an account and plan to the Academy of Sciences, of a barge moved by a wheel placed on each side of the boat." Tom. vi. p. 41, Machines Approuvées.

teen or fifteen hundred tons, they would impel it at the rate of three knots an hour."

Gensanne describes his engine as combining the improvements which made Newcomen's a selfacting machine, with a greater simplicity of parts than had been used when constructing an apparatus on Savery's principle: a, is a receiver; b, pipe from cistern; d, injection-pipe and cock; e, f, the lever of the steam or regulating valve; ≈, g, the fork which moves it backwards and forwards; h, k, parallel levers; i, lever moving on an axis; o, attached to parallel rods; m, n, tumbling-bobs; r, s, boxes attached to each end of lever i, each having a valve opening upwards to allow the water with which they are filled to escape. The rise and fall of a tappet or sliderpin fixed in the rod, h, which is inserted in the slider, forming the continuation of the lever or axis of injection-cock; x, boiler. In the engraving the parts are shown in the position of the injection-cock, being open, and the steam-cock shut, and the receiver filled with water. At this instant the mechanism is so arranged that the water. box, s, is empty, and the opposite one, r, is filled to its limit with water: the end of the lever on which it is fixed preponderates, and it moves downwards, (the valve in the bottom of the cistern from which it was filled, closes of itself by the weight of water on it.) The slider of the injection-cock is also moved downwards, which closes it; and during the same moment, the fork reverses the position of the steam-valve, and opens it; approaching nearly to the limit of its stroke, the lever comes in contact with the arm of the tumbling-bob, n, and raising its weight beyond the

P. 14, Specimina Ichnographica.

200

HULLS' STEAM-BOAT.

perpendicular, receives a sharp impulse from its quick fall; this completes the operation. At this instant a spindle of the valve in the bottom of the box,r, is thrust upward, and the water which it contained escapes through it;-and at the same moment the box, s,which had been elevated by the rise of the other end of the lever, thrusts the spindle of the valve, placed in the bottom of the cistern also upward; and receives the water which falls from it. When it is filled, the preponderance which is given to the end of the lever on which it is fixed carries it downwards. This reverses the position of all the other parts,* and it is obvious the movement may be repeated.

Another mode of applying the power of a steamengine to navigate a vessel, was suggested by Jonathan Hulls in 1737. But the scheme, although a nearer approach to the present form of the steam-boat than Allen's, can neither be considered as the first suggestiou for moving wheels by steam, nor any improvement on the idea which emanated from another-nor even any specimen of mechanical skill, for it is awkward, clumsy, and inartificial; but, as his claims have been put forth to a higher place than is here assigned him, they will be better understood by a reference to the engraving marked HULLS, 1737, and the description of it which follows nearly in his own words. It is doubtful whether Hulls ever proceeded beyond printing a description of his project.

* P. 222, vol. vii. Machines Approuvées.

A description and draught of a new-invented machine for carrying vessels or ships out of or into any harbour, port, or river, against wind or tide; or in a calm. Lond. 1737. It is a pamphlet, by no means scarce, containing forty-eight pages, about eight of which have any reference to his iuvention. Hulls took out a patent.

+ See page 97.