78 PHILOSOPHICAL TRANSACTIONS. [aNNO 177^- 



ready for use ; and with it were tried the following experiments, each of which 

 was repeated so many times as to be fully satisfactory. 



Table of Experiments, 



The 58-i.* in number 3, column /, was determined in fact from 29^% being 

 tlie time of making 10 ec|uable revolutions, after the weight was dropped off, in 

 order to prevent the sensible retardation that miglit take place, and affect the ob- 

 servation, if continued for 20 revolutions made so slowly. 



I have already detinetl what I mean by mechanic power ; but, before proceed- 

 ing further, it will be necessary also to define the following terms: 



Impulse or impulsion, impulsive force or power, impelling force or power, by 

 all which, I understand the uniform endeavour that one body exerts on another, 

 in order to make it move ; and that, whether it produces or generates motion by 

 this endeavour or not ; and the quantity of this impelling power may be mea- 

 sured either by its being a weight of itself, or by being counter-balanced by a 

 weight. It may also act either immediately on the body to be moved, so that if 

 motion is the consequence, they move with the same velocity; and that, either 

 by a simple contact, or by being drawn as by a cord, or pushed as by a staff: or 

 it may act by the intervention of a lever or other mechanic instrument, in which 

 the velocity of the body to be moved may be very different from the velocity of 

 the impelling power or mover ; but in comparing them, the impelling powers 

 must be reduced according to the proportional velocities of the mover and 

 moved ; or, in levers of different lengths, they may be compared by a standard 

 length of lever, which is the method taken in the subsequent reasoning on the 

 preceding experiments. An impelling power therefore, consisting of a double 

 weight, or requiring a double weight to counter-balance it, when acting with 

 equal levers, is a double impelling power, or an impelling power of double the 

 intensity. 



Observations and Deductions from t he preceding Experiments. — 1st. By the 

 1st experiment it appears, that the mechanic power employed, consisting oi' 8 



