248 Experimental Philosophy. [Lecture 16. 



and, consequently, one ounce at P will balance 

 sixty ounces hung upon a tooth q in the ho- 

 rizontal diameter of the wheel. Then if the 

 diameter of the wheel F be ten times as great as 

 the diameter of the axle G, the wheel will have 

 ten times the velocity of the axle ; and therefore 

 one ounce P at the end of the lever AB will 

 balance ten times sixty, or six hundred ounces 

 hung to the rope H which goes round the axle. 

 Lastly, if four pulleys are added, they will make 

 the velocity of the lower block K, and weight 

 W, four times less than the velocity of the axle ; 

 and this being the last power in the machine, 

 which is four times as great as that gained by the 

 axle, it makes the whole power of the machine 

 four times six hundred, or two thousand four 

 hundred. So that if a man could lift one hun- 

 dred weight in his arms by his natural strength, 

 he would be able to raise two thousand four hun- 

 dred times as much, or 120 ton weight, by this 

 engine. But it is here as in all other mechanical 

 cases ; for the time lost is always as much as the 

 power gained, because the velocity with which 

 the power moves will ever exceed the velocity with 

 which the weight rises, as much as the intensity 

 of the weight exceeds the intensity of the power. 

 The friction of the screw itself is very consi- 

 derable ; and there are few compound engines 

 which will not, upon account of the friction of 

 the parts against one another, require a third 

 part more of power to work them when loaded. 



