656 PHILOSOPHICAL TRANSACTIONS. [ANNO 1785. 



tried, and the descent was always found too soon in the former, and too late in 

 the latter case ; by which I was assured that the spaces first mentioned corres- 

 ponded exactly to the times. And, for the greater certainty, each descent was 

 repeated 8 or 10 times ; and every caution used in this experiment was also made 

 use of in all the following. 



Exper. 2. A 2d body was laid on the horizontal plane, and a moving force 

 applied which descended 4 If inches in 3 s ; the stage was then adjusted to the 

 space corresponding to 2 s , on supposition that the spaces descended through were 

 as the squares of the times, and it was found to agree accurately with the time ; 

 the stage was then adjusted to the space corresponding to I s , on the same suppo- 

 sition, and it was found to agree with the time. 



Exper. 3. A third body was laid on the horizontal plane, and a moving force 

 applied, which descended 59f inches in 4 s ; the stage was then adjusted to the 

 space corresponding to 3 s , on supposition that the spaces descended through 

 were as the squares of the times, and it was found to agree with the time ; the 

 stage was then adjusted to the space corresponding to 2 s , on the same supposi- 

 tion, and it was found to agree with the time ; the stage was then adjusted to 

 the space corresponding to I s , and was found to agree with the time. 



Exper. 4. A 4th body was then taken and laid on the horizontal plane, and a 

 moving force applied, which descended 55 inches in 4"; the stage was then ad- 

 justed to the space through which it ought to descend in 3 s , on supposition that 

 the spaces descended through were as the squares of the times, and it was found 

 to agree with the time ; the stage was then adjusted to the space corresponding 

 to 2 s , on the same supposition, and was found to agree with the time; lastly, the 

 stage was adjusted to the space corresponding to I s , and it was found to agree 

 exactly with the time. 



Besides these experiments, a great number of others were made with hard 

 bodies, or those whose parts so firmly cohered as not to be moved inter se by 

 the friction ; and in each experiment bodies of very different degrees of friction 

 were chosen, and the results all agreed with those related above ; we may there- 

 fore conclude, that the friction of hard bodies in motion is a uniformly retarding 

 force. 



But to determine whether the same was true for bodies when covered with 

 cloth, woollen, &c. experiments were made in order to ascertain it ; when it was 

 found in all cases, that the retarding force increased with the velocity ; but on 

 covering bodies with paper, the consequences were found to agree with those 

 related above. 



4. Having proved that the retarding force of all hard bodies arising from fric- 

 tion is uniform, the quantity of friction, considered as equivalent to a weight 

 without inertia drawing the body on the horizontal plane backwards, or acting 



