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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    Put the power impelling each half wedge will be to the refiftance of the block againft its fide, as the thicknefs of that half wedge is to its perpen- dicular height, becaufe the block will be driven off perpendicularly to the fide of the bar AB. Therefore the power to drive both the half wedges is to both the refiftances, as both the half backs is to the perpendicular height of each half wedge. And if the bar be taken away, the blocks put clofe together, and the two half wedges joined to make one; it will require as much force to drive it down between the blocks, as is equal to the fum of the feparate powers a&ing upon the half wedges when the bar was between them. To confirm this by an experiment, let two Fig cylinders, as\AB and CD, be drawn toward one another by lines running over fixed pulleys, and a weight of 40 ounces hanging at the lines be- longing to each cylinder : and let a wedge of 40 ounces weight, having its back juft as thick as either of its fides is long, be put between the cylinders, which will then aft againft each fide with a refiftance equal to 40 ounces, while its own weight endeavours to bring it down and feparate them. And here, the power of the wedge’s gravity impelling it downward, will be to the refiftance of both the cylinders againft the wedge, as the thicknefs of the wedge is to double its perpendicular height; for there will then be an equilibrium between the weight of the wedge and the refiftance of the cylinders againft it, and it will remain at any height between them ; re- quiring juft as much power to pufh it upward as to pull it downward—If another wedge of £°?ht Snd depth with this’ and onlY half as thick, be put between the cylinders, it will require twice as much weight to be hung at the ends