VOL. LXXV.] PHILOSOPHICAL TRANSACTIONS. 655 



to the cases for which they were intended. I therefore endeavoured by a set of 

 experiments to determine, 



1st, Whether friction be a uniformly retarding force. 



'2dly, The quantity of friction. 



3dly, Whether the friction varies in proportion to the pressure or weight. 



4thly, Whether the friction be the same on whichever of its surfaces a body 

 moves. 



The experiments, in which I was assisted by my ingenious friend the Rev. 

 Mr. Jones, Fellow of Trinity College, were made with the utmost care and at- 

 tention, and the several results agreed so very exactly with each other, that I do 

 not scruple to pronounce them to be conclusive. 



2. A plane was adjusted parallel to the horizon, at the extremity of which was 

 placed a pulley, which could be elevated or depressed in order to render the string 

 which connected the body and the moving force parallel to the plane. A scale 

 accurately divided was placed by the side of the pulley perpendicular to the hori- 

 zon, by the side of which the moving force descended ; on the scale was placed 

 a moveable stage, which could be adjusted to the space through which the 

 movino- force descended in any given time, which time was measured by a well 

 regulated pendulum clock vibrating seconds. Every thing being thus prepared, 

 the following experiments were made to ascertain the law of friction. But let 

 me first observe, that if friction be a uniform force, the difference between it 

 and the given force of the moving power must be also uniform, and therefore 

 the moving body must descend with a uniformly accelerated velocity, and conse- 

 quently the spaces described from the beginning of the motion must be as the 

 squares of the times, just as when there was no friction, only they will be dimi- 

 nished on account of the friction. 



3. Exper. 1. A body was placed on the horizontal plane, and a moving force 

 applied, which from repeated trials was found to descend 52-J- inches in 4 s ; for 

 by the beat of the clock, and the sound of the moving force when it arrived at 

 the stage, the space could be very accurately adjusted to the time ; the stage was 

 then removed to that point to which the moving force would descend in 3 s , on 

 supposition that the spaces described by the moving power were as the squares of 

 the times ; and the space was found to agree very accurately with the time ; the 

 stage was then removed to that point to which the moving force ought to descend 

 in 2 s , on the same supposition, and the descent was found to agree exactly with 

 the time; lastly, the stage was adjusted to that point to which the moving force 

 ought to descend in I s , still on the same supposition, and the space was ob- 

 served to agree with the time. Now, in order to find whether a difference in 

 the time of descent could be observed, by removing the stage a little above and 

 below the positions which corresponded to the above times, the experiment was 



