NEWTON S PRINCIPIA. 237 



and wax when rarefied is not instantly reduced by cold to 

 its former density. Before they were let fall, they were 

 totally immersed in water, lest, by the weight of any part 

 of them that might chance to be above water, their descent 

 should be accelerated in the beginning. Then, when after 

 their immersion they were perfectly at rest, they were let 

 go with the greatest caution, that they might not receive 

 any impulse from the hand that let them down. At 

 Newton s first experiments the weather was a little colder 

 than when the globes were weighed, and therefore he 

 repeated the experiments another day. On making the 

 experiments several times over, he found that the globes 

 fell mostly in the times of 49 J to 50 oscillations, the times 

 varying, however, from 47-| to 53 oscillations. On com 

 puting from the theory the time of descent, it was found 

 to be 50 oscillations, very nearly. Newton tried eight 

 other sets of experiments, in all of which there was a 

 tolerable accordance between theory and experiment. The 

 times in which the balls descended varied, sometimes 

 as much as one-fifth of the whole time of descent ; but the 

 errors were generally as much on one side as on the other 

 of the theoretical result. Whence, for such swift motions 

 as these, we may conclude that the resistance on a globe 

 is very nearly represented by the preceding theory. 

 Those globes which fell with a slower motion were found 

 to agree best with the theory, and the reason of this is as 

 follows. When the globes were first let fall, it was found 

 that they oscillated about the centre, that side which is 

 heaviest tending to descend first. The globe in conse 

 quence of these oscillations communicated a greater motion 

 to the fluid than it otherwise would, that is, it met with 

 a greater resistance. In the heavier and larger globes this 

 oscillation was not checked by the water until after several 

 oscillations, and hence these were more resisted than the 



