OF SIMPLE ACCELERATING FORCES. 79 



Scholium 1. The v of Laplace is sometimes em- 

 ployed as denoting the number of metres described in a 

 decimal second, or -864% which is also the number of my- 

 riometers described in a decimal hour, or the tenth of a 

 day (§ 4. P. 15.) : but it is often more convenient for com- 

 putation to make v the number of English feet described 

 in an ordinary second. 



Scholium 2. The machine, invented by Mr. Atwood, 

 furnishes us with a very convenient mode -of making expe- 

 riments on accelerating forces. The velocity, produced by 

 the undiminished force of gravity, is much too great to be 

 conveniently submitted to experimental examination ; but 

 by means of this apparatus, we can diminish it in any degree 

 that is required. Two boxes, which are attached to a 

 thread passing over a pulley, may be filled with different 

 weights, which counterbalance each other, and constitute, 

 together with the pulley, an inert mass, which is put into mo- 

 tion by a small weight added to one of them. The time of 

 descent is measured by a second or half second pendulum, 

 the space described being ascertained by the place of a 

 moveable stage, against which the bottom of the descend- 

 ing box strikes : and when we wish to determine immedi- 

 ately the velocity acquired at any point, by measuring the 

 space uniformly described in a given time, the accelerating 

 force is removed, by means of a ring, which intercepts the 

 preponderating weight, and the box proceeds with a uniform 

 velocity, except so far as the friction of the machine retards 

 it. By changing the proportion of the preponderating 

 weight to the whole weight of the boxes, it is obvious that 

 we may change the velocity of the descent, and thus exhi- 

 bit the effects of forces of different magnitudes. Now, 

 that the velocity generated is proportional to the time of the 

 action of the force, or that the force of gravitation, at least 



