VOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. 173 



more hours going, the two pendulums did not vary a quarter of a second in 

 the open air^ or when the unexhausted receiver was put over the little move- 

 ment ; yet when the receiver was exhausted, the half seconds movement would 

 lose, at the rate of two seconds in every hour, in every experiment, in many 

 hours going. 



In order to see what alterations would arise from varying the vibrations, by 

 opening and shutting the pallets, I caused the vibrations in some experiments 

 to be as large as the receiver would bear ; in others, to be as short as possible ; 

 always adjusting the pendulum to vibrate half seconds nicely in the air. Yet 

 still the success was much the same, or the difference was scarcely perceptible. 

 Only I imagined, when the pendulum vibrated but a little way from the per- 

 pendicular, that the vibrations in vacuo were not so much enlarged, as when it 

 vibrated in a larger arch. 



In all these experiments, repeated many times with the same success, I had 

 no reason to think, but that the vibrations were enlarged in vacuo by the vast 

 rarefaction of the medium ; only, that perhaps the different state of the air 

 might alter the force of the spring, which drove the movement. For the trial 

 of this, I put a well adjusted pocket-watch, with Hook's regulator, i. e. the 

 common small spiral spring to the balance, into the vacuum. And after several 

 trials, at the same pitch of the spring, I found not the least alteration in the 

 watch's going in many hours ; neither the springs, nor any other part of the 

 watch seeming to be in the least affected by the vacuum ; the balance circum- 

 volving, or keeping the same turns, as in the open air. 



But to be still more sure, if possible, I tried what would be the success by 

 putting the half-seconds pendulum again into the receiver, and only pumping 

 out a part of the air. And accordingly I left no more air in, than what kept 

 the included mercurial gauge at about Q inches height. The event of which 

 was, that the vibrations were then not above -^ inch larger on each side, than 

 in the unexhausted receiver ; and the time lost, but about half a second in an 

 hour, or 4 at most. And so, according as the mercurial gauge was more or 

 less high, I always found the vibrations greater or less ; always gradually de- 

 creasing, according to the quantity of air re-admitted. 



From these experiments the following remarks have occurred. 1, That what 

 Mr. Boyle long since observed (from a cocked pistol going down as fiercely in 

 his vacuum, as in the air) may be hereby further confirmed, viz. that the air is 

 not the cause of the motion of restitution in solid bodies, as springs. For if 

 it was, it would certainly have been discovered in so tender an instrument 

 as a well adjusted pocket-watch, lying under the perpetual influence of |wo 

 springs. 



