Some wheels are destined to effect certain objects without increase of power, as in clocks or watches. Sometimes, a greater power is applied to produce increased motion, as in the roasting jack, and in many mills.

Obs. On duly considering the vast increase of power by some of these combinations, it cannot be matter of further wonder that first-rate men of war, and other such vast objects, are easily constructed. In some instances, one man is enabled to lift as much as 1000, and powers may be applied equal to the strength of a hundred thousand men.

176. Clocks and watches are nothing more than a simple arrangement of wheels of different diameters and numbers of teeth, so as to indicate seconds, minutes, hours, days, and even months.

Clocks are set in motion by a weight which turns a cylinder, which cylinder sets the whole in motion.

Watches are kept in motion by a coiled spring, which, in seeking to uncoil itself, exerts a power that gives motion to one wheel, which turns all the others.

Obs.-A lecture of ten minutes at a watch-maker's, with the wheels and other parts under the eye, will explain more than could be done by verbal description in a volume.

177. The triumph of mechanics is the steamengine. The inventor observed the excessive . force of steam in lifting up the stiff lid of a kettle as he sat at breakfast, and he and others have since applied this resistless power to produce a motion applicable to all kinds of machinery.

178. In constructing these engines, steam from a copper is thrown into a hollow iron cy

F

linder, with a close lid or stopper, which rises as the steam rushes into the cylinder, and falls, when the steam is condensed by cold water thrown in for the purpose.

An upright iron rod is fixed to that lid, and to one end of a large beam; which, in consequence, has an action communicated to it similar to that of a see-saw, and is lifted up and pulled down, with wonderful precision and force."

THE STEAM ENGINE.

Obs. 1.-A regular and powerful motion being thus produced, the mechanic seizes upon it, and applies it with ease to all kinds of machinery. The apparatus itself has been slightly varied by different persons, and for different objects; but the principle remains the same, . and it is, perhaps, the greatest discovery that ever was made in mechanics.

2.-Mr. Watt, of Birmingham, has made many improvements in the steam-engine; and, among others, he fastens the top of the cylinder, working the rod through it, and injects steam above as well as below, so that the motion downward is produced by steam, as well as that upward; he also condenses the steam in an adjoining

vessel. One horse can, by common machinery, raise 25,000 pounds one foot high in a minute; but some steam machines perform the labour of 60 or 80 horses! A small one of a ten-horse power, with the steam produced by a single bushel of coals, will raise 30,000,000 of pounds one foot high; or it will grind and dress three sacks of wheat, slit and draw into nails five cwt. of iron, and drive at the same time 1000 cotton spindles. Steam-engines have lately been applied with success, to impel boats and ships.

3.-Mr. Blenkinsop, of Leeds, has lately applied steam to move coal waggons on a rail-way, instead of drawing them with the power of horses, with great success. Here is represented his machine, to which any carriage may be annexed.

BLENKINSOP'S MACHINE.

C. C. Crank Rods.

⚫ D. D. Steam Cylinder.
E. Discharging Pipe.
F. Smoke Chimney.
G. Fire Door.

Scale one-eighth of an inch to a foot.

179. The Pump for raising water is a very useful machine; and its principle should be understood. It can raise water, if required, to the height of thirty-three feet, by the pressure of the air on the water; and is founded on the principle of the elasticity or pressure of air.

Obs. If a long glass tube closed at one end, were deprived of air, and its open end immersed in quicksilver, the quicksilver will rise in it about 29 inches; or if placed in water, 33 feet of water will rise in it, the weight of 33 feet of water, being equal to 29 inches of quicksilver. The rise of those fluids in such a tube, is caused by the pressure of the air on the surface of the external mercury or water: hence, it is inferred, and with reason, that the elasticity of the air which we breathe, is in all places equal in force to the weight of about 29 inches of mercury, or 33 feet of water.

180. To raise water 33 feet high, nothing more then is requisite than to put one end of a pipe in it, and to draw the air out of that pipe, when the water will instantly ascend in the pipe.

Such is the purpose and effect of a pump; and all that is to be done is by proper contrivances to draw out the air above, and keep up a supply of the water below.

181. A pump consists of a wooden or copper pipe, with a long iron rod to work up and down within it, by means of a handle.

At the lower end of the iron rod is fixed a metallic hoop, provided with leather to fit the pipe: in the centre of the hoop is a little trap-door or valve, which opens only upwards, and when down, shuts very close.

At the bottom of the pipe, near the water, año

ther such valve also opening upwards, is fixed tight within the pipe itself.

182. The handle of the pump being raised, the iron rod (called the piston,) with its valve at the bottom of it, is forced down the pipe.

As the valve opens upwards, the air in the pipe passes up through the valve.

On pulling down the handle, the piston is raised, and with it the valve, leaving a vacuum or vacuity between it and the lower fixed valve.

To fill up the vacuum, the water rushes up through the lower valve.

On again raising the handle, the piston again descends; and the water now rushes through its valve, and on pulling down the handle again, the piston and its closed valve rise, bringing up

the water.

Its ascent creates a new vacuum, and other water rushes through the lower valve; the upper valve is made to descend again, to rise again closed, and bring up water.

183. Fire-engines, and other forcing-engines, have no valve or flap fixed to the piston; but a solid plate is moved up and down by it, and the rising water is thus violently driven into an adjoining air-tight vessel.

Through the top of that vessel, the playing pipe is so inserted, that its mouth may lie below the water, leaving the upper part of the vessel filled with air.

Then the elastic power of that portion of air, forces the driven water up the playing pipe. The energy of the stream, will of course de