r>0 MECHANIC POWERS. 



crum of the lever, and consequently act with less 

 force upon it ; but if it be placed in the position 

 E F, the line of direction will fall farther from the 

 fulcrum, and therefore act more on the lever. 



On the contrary, it is evident from fig. 12. that 

 opposite effects take place, when the weight is 

 below the lever. 



Nothing of this kind can happen, when the 

 weight is suspended from the lever by a rope, be- 

 cause the point of suspension, or point of action, 

 is not altered. 



When two draymen carry a barrel on a coulstaff, 

 to which it is suspended by a chain, the point on 

 which the w r eight acts not being altered by inclin- 

 ing the staff in going up or down hill, there will 

 be no variation in the weight that each man had 

 to support on beginning. But if they carry the 

 barrel upon two dogs, then the weight does not 

 sw T ing, and the centre of gravity is below the lever ; 

 therefore the point on w r hich the weight acts, will, 

 by inclining the lever, be made to approach the 

 highest end ; and the first man, in going down 

 hill, by having this point removed from him, will be 

 eased in part of his burden ; and the last man will 

 have his equally increased. 



Hitherto we have supposed that the power and 

 weight acted perpendicularly upon the lever ; but 

 if they do not, they act with less force upon it ; 

 the power should, therefore, if possible, be always 

 made to act at right angles to the lever. 



If several levers be combined together in such a 

 manner, as that a weight being appended to the 

 first lever, may be supported by a power applied 

 to the last, as in Plate 1. fig. 13. which consists of 

 three levers of the first kind, and is so contrived, 

 that a power applied at the point L of the lever C, 



9 



