Hand-books of Natural Philosophy and Astronomy: Mechanics. Hydrostatics, hydraulics, pneumatics, and sound. Optics.- v. 2. Heat. Magnetism, common electricity, and voltaic electricity.- v. 3. Meteorology. Astronomy

Blanchard and Lea, 1851

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Página 521 - When a ray of light passes from one medium to another, it is refracted so that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is equal to the ratio of the velocities in the two media.
Página 93 - Every body must persevere in its state of rest, or of uniform motion in a straight line, unless it be compelled to change that state by forces impressed upon it." II. " Every change of motion must be proportional to the impressed force, and must be in the direction of that straight line in which the force is impressed.
Página 25 - ... of an ounce. But we need not stop even here. This portion of the wire may be viewed through a microscope which magnifies 500 times; and by these means, therefore, its 500th part will become visible.
Página 345 - Thus, if fair weather follow immediately the rise of the mercury, there will be very little of it, and, in the same way, if foul weather follow the fall of the mercury, it will last but a short time. (4.) If fair weather continue for several days, during which the mercury continually falls, a long succession of...
Página 345 - TLe following rules may to some extent be relied upon, but even these are subject to much uncertainty. 1. Generally the rising of the mercury indicates the approach of fair weather, the falling of it shows the approach of foul weather. 2. In sultry weather, the fall of the mercury indicates coming thunder. In winter the rise of the mercury indicates frost. In frost, its fall indicates thaw, and its rise indicates snow.
Página 207 - ... theory, viz., the friction which arises between its surface and the substance which it divides. This is the case when pins, bolts, or nails, are used for binding the parts of structures together ; in which case, were it not for the friction, they would recoil from their places, and fail to produce the desired effect. Even when the wedge is used as a mechanical engine, the presence of friction is absolutely indispensable to its practical utility. The power...
Página 208 - The power, as has already been stated, generally acts by successive blows, and is therefore subject to constant intermission, and, but for the friction, the wedge would recoil between the intervals of the blows with as much force as it had been driven forward.
Página 184 - The treddle of the turning lathe is a lever of the third kind. The hinge which attaches it to the floor is the fulcrum, the foot applied to it near the hinge is the power, and the crank upon the axis of the fly-wheel, with which its extremity is connected, is the weight. Tongs are levers of this kind, as also the shears Used in shearing sheep. In these cases the power is the hand placed immediately below the fulcrum or point where the two levers are connected.
Página 226 - Some engines used in coining have flies with arms four feet long, bearing one hundred weight at each of their extremities. By turning such an arm at the rate of one entire circumference in a second, the die will be driven against the metal with the same force as that with which 7500 pounds weight would fall from the height of 16 feet ; an enormous power, if the simplicity and compactness of the machine be considered.

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