Analysis of a course of lectures : on mechanics, hydrostatics, pneumatics, and astronomy / read by James Ferguson.

  • James Ferguson
Date:
1761
Catalogue details

Licence: Public Domain Mark

Credit: Analysis of a course of lectures : on mechanics, hydrostatics, pneumatics, and astronomy / read by James Ferguson. Source: Wellcome Collection.

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    C 6-J A lever Is faid to be of the firft kind, when the prop is between the weight and the power.—Here, the power and weight balance each other* when the power is in proportion to the weight, as the diilance of the weight from the prop is to the diilance of the power from it. Of this fort are our iron crows* fciffars, pincers, fnuffers, and the like. A lever is faid to be of the fecond kind, when the weight is between the prop and the power.—Here* the power and weight balance each other* when the power is in proportion to the weight, as the diilance of the weight (or refiftance) from the prop is to the diftance of the power from it. Of this fort are doors turning on hinges, rudders of fhips, oars* and fuch cutting knives as are fixed at the point. A lever is laid to be of the third kind, when the power is between the weight and the prop. In this, the power and weight balance each other, when the power is in proportion to the weight, as the diilance of the weight from the prop is to the diilance of the power from it. Of this fort are the bones of our legs and arms, and the wheels of clocks and watches. The bended lever differs in nothing but its form from a lever of the firil kind : its power is the fame, and is applicable to that of a hammer drawing a nail. In the wheel and axle, the velocity of the power is to the velocity of the weight, as the circumference of the wheel is to the circumference of the axle; and the advantage gained by this machine is diredlly in the fame proportion: for the power and weight balance each other, when the power is in proportion to the weight, as the circumference of the axle is to the circumference of the wheel. This machine is the principal part in a common crane. A pulley, that only turns on its axis, and does not rife with the weight, ferves only to change the direc¬ tion of the power j for it gives no mechanical advan¬ tage thereto. When,
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