80 On the Mutual Influence 



far as I can gather, there is a considerable difference in the cir- 

 cumstances under which they were made. 



Mr. Ellicott appears to have confined his experiments to a 

 fixed medium between the two clocks, viz., the base on which 

 they stood, or the fixed rail by which they were supported. I 

 have conducted my investigations with media of different hinds 

 and dimensions, varied as much as the limited amount of time 

 devoted to them would admit of. 



The balls of each of the pendulums employed by the former 

 weighed 23 lbs. ; the cisterns of mercury in my clocks weigh 

 respectively 10 lbs. and 8-|lbs ; the clock- weights themselves are 

 each of them 9 lbs. and the clocks are superior mean time clocks 

 ordinarily employed in the work of the Observatory. 



The total number of experiments is forty, and in making them, 

 every care and precaution was taken. 



For the sake of convenience I shall designate these clocks as 

 No. 1 and No. 2, the latter being the one originaily at rest ; the 

 former, the one set in motion by the hand. 



The only foundation which, at the time, could be made avail- 

 able for the experiments was a stone slab, detached from the floor, 

 on which the clock No. 1 usually rests. As there was not room 

 enough for both clocks on this slab, a solid plank of well-seasoned 

 cedar, weighing about 17 lbs., was placed on it, and the position 

 of the clocks upon it so arranged that there was no unequal 

 pressure on any part of the stone slab. 



In detailing the experiments, I propose on the present occasion, 

 to select one only from each of the important groups — consider- 

 ing that one as a fair type of the whole. 



Exp. 1. — In the first experiment, clock 1 was placed on the 

 stone slab, and clock 2 on the floor, but quite unconnected with 

 the stone — the interval being about one inch. The pendulum of 

 1 was made to oscillate through an arc of 6 degrees. Clock 2 

 was watched for about 70 minutes, but there was no appearance 

 of motion. 



This experiment was instituted for the purpose of determining 

 Avhether any effect was produced by the mutual attraction of the 

 pendulums, independently of a connecting medium. 



Exp. 2. — In experiment 2 the circumstances were as in the 

 last case, only that clock 2 was brought into close contact with 

 the stone slab on which clock 1 rested. There was no perceptible 

 eftect. 



Exps. 3 and 4. — In experiments 3 and 4, both clocks were 

 placed on the solid plank, as before described. The bases of the 

 clocks were first placed about f inch apart, and then brought into 

 contact. In neither experiment was the slightest effect per- 

 ceptible. 



In all these experiments it will be o'Dserved that there was no 

 upper medium. 



