Lectures on select subjects in mechanics, hydrostatics, hydraulics, pneumatics, and optics, with the use of the globes, the art of dialing, and the calculation of the mean times of new and full moons and eclipses / By James Ferguson.

  • Ferguson, James, 1710-1776.
Date:
1803
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on select subjects in mechanics, hydrostatics, hydraulics, pneumatics, and optics, with the use of the globes, the art of dialing, and the calculation of the mean times of new and full moons and eclipses / By James Ferguson. Source: Wellcome Collection.

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    working power. Thus, if one end of the rope KMOk^ be fixed to a hook at /, and the rope pafles over the pulleys N and R, and under the pulleys L and P, and has a weight T, of one pound, hung to its other end at T, this weight will balance and fupport a weight W of four pounds hanging by a hook at the moveable block U, allowing the faid block as a part of the weight. And if as much more power be added, as is fufficient to overcome the fridtion of the pulleys, the power will defcend with four times as much velocity as the weight rifes, and confe- queritly through four times as much fpace. The two pulleys in the fixed block X, and the two in the moveable block T, are in the fame cafe with thofe laft mentioned ; and thofe in the lower block give the fame advantage to the power. As a fyftem of pulleys has no great weight, and lies in a fmall compafs, it is eafily carried about; and can be applied in a great many cafes, for raifing weights, where other engines cannot. But they have a great deal of fri&ion on three accounts: l. Becaufe the diameters of their axes bear a very confiderable proportion to their own diameters; 2. Becaufe in working they are apt to rub againft one another, or againft the Tides of the block ; 3. Becaufe of the ftiffnefs of the rope that goes over and under them. 4. i he fourth mechanical power is the in- The in- dined, plane,, and the advantage gained by it is dined as great as its length exceeds its perpendicularfiane- height. Let AB be a plane parallel to the hori- Vr zon, and CD a plane inclined to it; and fuppofe Fie. 1. the whole length CD to be three times as great as the perpendicular height G/P; in this cafe, vne cylinder E will be fupported upon the plane . CD,