OUTLINES OF NATU11AL PHILOSOPHY. 



167. The effect of friction may be diminished, 

 by drawing a body in a line inclined at a certain 

 angle to the plane on which it rests. Thus, if the 

 weight of a body be to its friction, on a horizon- 

 tal plane, as ft to 1, it will be drawn with the 

 greatest ease in the direction which makes with 



that plane an angle, having for its tangent - . 



ft 



DAN. BERNOUILLI, Nov. Com. Petrop. torn. 13. p. 244. 



168. Friction is diminished, when it is converted, 

 by means of wheels or rollers, from the friction of 

 sliding into that of rolling bodies. 



When each end of the axis of a wheel is made to turn, 

 not in a groove, but on the circumferences of two 

 wheels, every one moveable on its own axis, these 

 last are called Friction Wheels, as serving very much 

 to lessen the effect of friction. 



169. The momentum of friction is diminished 

 by friction wheels, in the ratio of the radius of the 

 axis of any one of the wheels (they are supposed 

 equal) to the perpendicular height of the axis that 

 rests upon them, above the line joining their 

 centres. 



EULER treats of the advantage of friction wheels, Mem. 

 Acad. Berlin, 1743, p. 144. The theorem he has 

 investigated is not so simple as the preceding, but 

 may be reduced to it. In the Phil. Trans, vol. LIII. 



p. 155. 



