to produce a continuous circular motion by means of ratchet wheels, similar to those previously used by Mr. Oxley, at Hartley colliery; to which, however, Mr. Wasbrough added a fly-wheel to maintain and regulate the motion. Several machines were constructed under this patent; and among others, one was erected at Mr. Taylor's saw-mills and block manufactory at Southampton. In 1780, one was erected at Birmingham, where the ratchet work was found to be subject to such objections, that one of the persons about the works substituted for it the simple crank, which has since been invariably used. A patent was taken out for this application of the crank in the same year, by Mr. James Pickard, of Birmingham. It will presently appear, however, that the suggestion of this application of the crank was derived from the proceedings of Watt, who was at the same time engaged in similar experiments.

(111.) The single-acting steam engine, as constructed by Watt, was not adapted to produce continuous uniform motion of rotation, for the following reasons:

First. The effect required was that of an uniformly acting force. The steam engine, on the other hand, supplied an intermitting force. Its operation was continued during the descending motion of the piston, but it was suspended during the ascent of the piston. To produce the continued effect now required, either its principle of operation should be altered, or some expedient should be devised for maintaining the motion of the revolving shaft during the ascent of the piston, and the consequent suspension of the moving power.

Secondly. The action of the steam engine was rectilinear. It was a power which acted in a straight line, viz., in the direction of the cylinder. The motion, however, required to be produced, was a circular motion-a motion of rotation around the axis or shaft of the mill.

upon

The steps by which Watt proceeded to accomplish these objects have been recorded by himself as follows, in his notes Dr. Robison's article on the steam engine:"I had very early turned my mind to the producing of continued motion round an axis; and it will be seen, by reference to my first specification in 1769, that I there described

a steam wheel, moved by the force of steam, acting in a circular channel against a valve on one side, and against a column of mercury, or some other fluid metal, on the other side. This was executed upon a scale of about six feet diameter at Soho, and worked repeatedly, but was given up, as several practical objections were found to operate against it; similar objections lay against other rotative engines, which had been contrived by myself and others, as well as to the engines producing rotatory motions by means of ratchet wheels. The Cincinnati papers announce the invention; made my single reciprocating engines very regular ya Mr. Solomans of that city, of a method of tents, I considered how to produce rotative moyoga as a motive power. The idea of a gem in the best manner; and amongst various explosive materials for purposes of locomotion were subjected to trial, or which passed prevented practical results. We quote the ind, none appeared so likely to answer the purblication of the crank, in the manner of the lathe; but as the rotative motion is produced to propel a boat across the ocean hade by impulse given to the crank in the descent heat in motion until it wears out. The key, it requires to be continued in its ascent by pressure of 540 pounds on the square inch, the wheel, which acts as a fly; being unwilling ater at the boiling point gives a prof gravity; ine with a fly-wheel heavy enough to continue With the addition of 30 degress of heat ring the ascent of the piston (or with a flynough to equalise the motion, even if a coun

gine is old: but hitherto the danger of using

llowing account from the local journal-Mr.

lomans, it is said, generates the gas from common hiting, sulphuric acid and water. "Five dollars orth of these materials," says the Nonparel,

zen times, and if there be no leakage it will keep

hile water has none, except that of

power is double, giving 30 pounds; and so on,

bling with every addition of 30 degrees of heat,

have 3,840 pounds

under a heat of

res, a heat which no engine can endure.

g

452 employed to act during that ascent), I proposed the gas 20 degrees of heat give engines, acting upon two cranks fixed on the degres gives 2,160 pounds; 80 degrees in angle of 120° to one another, and a weight he circumference of the fly-wheel at the same by converting water into steam of the cranks, by which means the motion

pounds; that is, 132 degrees less than

Ting heat gives, a greater power with this

result is, that it requires 1,800 dols. of expenseered nearly equal, and only a very light fly

run a boat to New Orleans and back again with

old engine, while this one will do the same e requisite.

rk for 50 dols.-Mr. Solomans has his engine in eration. It is of 25-horse power, and raises 900 pounds up and down five times in a minute. has it so planted that its power may be seen. engine is so constructed as to be self-sustaining,

occurred to me very early; but my attention mployed in making and erecting engines for it remained in petto until about the 1778

year

acturing and pumping its own gas, while a Mr. Wasbrough erected one of his ratchet

farmace, almost half as large as a common ace for heating flat-irons, furnishes all the heat at

desires. A handful of charcoal does the work, f which recalled the subject to my mind, and

Birmingham, the frequent breakages and

his boiler is about as large as a good-sized ball-We must hear more of this new pt to construct a gas engine before we attach credit to the accounts of our Transatlantic temporary.1.

make a model of my method, which answered hs; but having neglected to take out a patent, was communicated by a workman employed to

make the model, to some of the people about Mr. Wasbrough's engine, and a patent was taken out by them for the application of the crank to steam engines. This fact the said workman confessed, and the engineer who directed the works acknowledged it; but said, nevertheless, that the same idea had occurred to him prior to his hearing of mine, and that he had even made a model of it before that time; which might be a fact, as the application to a single crank was sufficiently obvious.

This

"In these circumstances, I thought it better to endeavour to accomplish the same end by other means, than to enter into litigation; and if successful, by demolishing the patent, to lay the matter open to every body. Accordingly, in 1781, I invented and took out a patent for several methods of producing rotative motions from reciprocating ones; amongst which was the method of the sun-and-planet wheels. contrivance was applied to many engines, and possesses the great advantage of giving a double velocity to the fly-wheel; but is perhaps more subject to wear, and to be broken under great strains, than a simple crank, which is now more commonly used, although it requires a fly-wheel of four times the weight, if fixed upon the first axis; my application of the double engine to these rotative machines rendered the counterweight unnecessary, and produced a more regular motion."

(112.) Watt's second patent here referred to, was dated 25th October, 1781, and was entitled "A patent for certain new methods of applying the vibrating or reciprocating motions of steam or fire engines to produce a continued rotative or circular motion round an axis or centre, and thereby to give motion to the wheels of mills and other machines."

All the methods specified in this patent were intended to be worked by the single-acting engine, already described, a counterweight being applied to impel the machinery during the returning stroke of the engine, which weight would be elevated during the descent of the piston. There were five different expedients proposed in the specification for producing a rotatory motion; but, of these five, two only were ever applied in practice.

(113.) Suppose a rod or bar attached by a pin or joint at the upper extremity to the working end of the beam of the engine, and by a similar pin or joint at the lower extremity to an iron wheel fixed on the extremity of the axis of the fly-wheel. One half of this wheel is formed of a solid semicircle of cast iron, while the other half is constructed of open spokes, so as to be as light as is consistent with strength. The position of the wheel on the axis is such that during the returning stroke of the piston, when the operation of the steam is suspended, the heavy semicircle of the wheel will be descending, and by its weight will draw down the connecting bar, and thereby draw down the working end of the beam, and draw up the piston in the cylinder. When the piston descends and is driven by the power of the steam, the heavy semicircle of the above-mentioned wheel will be drawn upwards, and in the same way the motion will be continued.

(114.) The second method of producing a rotatory motion, which was subsequently continued for many years in practical operation, was that which was called the Sun-and-planet Wheels.

A toothed wheel A (fig. 32.), called the sun wheel, was fixed on the axle of the fly-wheel, to which rotation was to be imparted. The wheel B, called the planet wheel having an equal diameter, was fastened on the end I of the connecting rod H I, so as to be

incapable of revolving. During the descent of the piston, the working end of the beam was drawn upwards, and the end I of the connecting rod travelled from c to D, through the dotted semicircle c I D. The wheel в not being capable of revolving on the centre I, would, during this motion, drive the sun wheel A. During the ascent of the steam piston, the working end of the beam would descend, and the centre I of

the planet wheel в would be driven downwards from D to C, through the other dotted semicircle, and would consequently continue to drive the sun wheel round in the same direction.

This contrivance, although in the main inferior to the more simple one of the crank, is not without some advantages; among others, it gives to the sun wheel double the velocity which would be communicated by the crank; for in the crank one revolution only on the axle is produced by one revolution of the crank, but in the sun-and-planet wheel, two revolutions of the sun wheel are produced by one of the planet wheel; thus a double velocity is obtained from the same motion of the beam. This will be evident from considering that when the planet wheel is in its highest position, its lowest tooth is engaged with the highest tooth of the sun wheel; as the planet wheel passes from the highest position, its teeth drive those of the sun wheel before them, and when it comes into the lowest position, the highest tooth of the planet wheel is engaged with the lowest of the sun wheel: but then half of the sun wheel has rolled off the planet wheel, and, therefore, the tooth which was engaged with it in its highest position, must now be distant from it by half the circumference of the wheel, and must, therefore, be again in the highest position; so that while the planet wheel has been carried from the top to the bottom, the sun wheel has made a complete revolution.

This advantage of giving an increased velocity may be obtained also by the crank, by placing toothed wheels on its axle. Independently of the greater expense attending the construction of the sun-and-planet wheel, its liability to go out of order, and the rapid wear of the teeth, and other objections, rendered it inferior to the crank, which has entirely superseded it.

(115.) Although by these contrivances Watt succeeded in obtaining a continuous circular motion from the reciprocating motion of the steam engine, the machine was still one of intermitting, instead of continuous action. The expedient of a counterweight, elevated during the descending stroke, and giving back the power expended on it in the interval of the returning stroke, did not satisfy the fas