Chap. 7-1 [ 55 ] 



CHAP. VII. 



OF THE MECHANIC POWERS. 



Sixjtmple Machines. The Lever. The Pulley. The moveahle Pul- 

 ley, Qf Wheels. Clockwork. Beft Mode of conducting the 

 Wheels of Carriages. The Wheel and Axle. The Crane. .The 

 Capjlan. The Crick or Jack, The inclined Plane. Motion of 

 Carriages up an inclined Plane, &c, The Wedge. The Screw. 

 The perpetual Screw. 



THE fcience of mechanics may poflibly be con- 

 fidered as in many refpedts foreign to a work, 

 which, as its title implies, was intended chiefly to de- 

 tail and explain the operations of nature. It muft be 

 remembered, however, thar the adtion of the mechanic 

 powers is the effect of thofe laws of motion which 

 have been explained in a preceding chapter, and that 

 even fome of nature's operations can fcarcely be well 

 underftood, without a previous acquaintance with thofe 

 principles by which bodies are moved with the great- 

 eft facility, and by which the animal machine in para- 

 cular is enabled to aft. 



There are fix funple machines or powers, of which 

 all the more complex engines are conftructed ; and 

 thefe are the lever, the pulley, the wheel and axle, the 

 inclined plane, the wedge, and the fcre-w. It has been 

 remarked by fome authors, that thefe fix machines 

 may in fa6t be refolved into two, the lever and the 

 inclined plane, for the pulley and the wheel and axle 

 may be confidered as compound levers, and the wedge 

 and the fcrew are only modifications of the inclined 

 plane, 



4 I. The 



