MECHANICAL POWERS. 67 



of which many stupendous erections, as massive statues, 

 lofty buildings, and various similar works of art, could 

 not have been effected. Man, in the early stage of 

 society, may be supposed to have soon discovered his 

 weakness, and to have directed his attention to the 

 attainment of artificial aid. It is natural to suppose that 

 the Lever would be the first power of which he availed 

 himself, as it is the most simple, and it is also that on 

 which all the other mechanical powers depend. 



The Mechanical Powers are six in number; viz., the 

 Lever, the Wheel and Axle, the Pulley, the Inclined 

 Plane, the H'edge, and the Screw : in the various com- 

 binations of these, all machines exist. 



The Lever is chiefly used to raise heavy weights to 

 small heights, as a handspike or crow, and is divided 

 into three kinds. A lever of the first kind, is when the 

 weight to be raised is at one end and the power at the 

 other, and the fulcrum, or prop, is between the two. 

 Thus, if a man be required to raise or remove a heavy 

 log of wood, he will thrust a handspike, or any similar 

 instrument, under the wood, and by placing another 

 piece of wood or stone as a fulcrum under the handspike, 

 and pressing down at the further end, he will probably 

 effect his purpose. If the log to be raised be Jive 

 hundred weight, and he can press with the force of one 

 hundred weight, he will be able to raise it by placing a 

 lever sir feet long over a fulcrum at one foot from the 

 weight to be raised, and pressing with the above-named 

 weight at the other end. For, as the distance of the 

 iceight from the fulcrum is to the distance from the ful- 

 crum to the power, so is the force applied to the effect 

 produced. 



It is a general rule in mechanics that what is gained 

 in power is lost in time ; so in the above there will be a 

 gain of power in proportion of Jive to one, but then the 

 hand of the operator will go over a space^u'e times that 

 of the log. The steelyard, used in weighing hay, meat, 

 and other things, is a lever of this kind. Pincers, snuff- 

 ers, scissors, &c., are also compound levers of this kind, 

 the joint round which they move being the fulcrum. 



A Lever of the second kind is when the fulcrum is at 



