( 438 ) 



2. Although HuYGRNs' obser\ atioiis were published in the Journal 

 des Scavans of 1665, and are moreover mentioned in his "Horologium 

 oscillatorium", thej seem to iiave been forgotten when in J 739 

 correlated phenomena were discovered by John Ellicott ^). What he 

 observed at first was this: of two clocks N". 1 and N°. 2 placed in 

 such a waj that their backs rested against the same rail ^), one, always 

 N°. 2, took over the motion of the other, so that after a timeN'.l 

 stopped even if at first N". 2 had been in rest and N". 1 exclusively 

 was set in motion. Later on he found that the mutual influence was 

 greatly increased by connecting the backs of the clocks by a piece 

 of wood '). He also made both clocks go on indefinitely by giving 

 their pendulums the greatest possible motion, when alternately they 

 took over a part of the motion from each other, according to a period 

 becoming longer as the clocks being placed without connection with 

 each other had a more equal rate ^). At the same time he observed 

 that both clocks when connected with each other in the way described 

 above assumed a perfectly equal rate lying between those which 

 they had each separately. 



3. Since then different mechanisms where suchlike phenomena 



Indeed, it is nothing but the friction which can finally cause that of the three 

 possible principal osc:llations only one remains. Every explanation in which friction 

 does not play a part must thus from the outset be regarded as insufficient. 



1) PliiL Trans. Vol. 51, p. 126—128: "An Account of the Influence which two 

 "Pendulum Clocks were observed to have upon each other," p. 128—135: 

 "Further Observations and Experiments concerning the two Clocks above mentioned." 



2) "The two Clocks were in separate Cases, and ... the Backs of them rested 

 "against the same Rail." 



'•J "I put Wedges under the Bottoms of both the Cases, to prevent their bearing 

 "against the Piail ; and stuck a Piece of Wood between them, just tight enough 

 "to support its own Weight." 



4) "Finding them to act thus mutually and alternately upon each other, I set 

 "them both a going a second time, and made the Pendulums describe as large 

 "Arches as the Cases would permit. During this Experiment, as in the former, I 

 "sometimes found the one, and at other times the contrary Pendulum to make the 

 "largest Vibrations. But as they had so large a Quantity of Motion given them 

 "at first, neither of them lost so much during the period it was acted upon by 

 "the other as to have its Work stopped, but both continued going for several 

 "Days without varying one Second from each other" . . . "Upon altering the Lengths 

 "of the Pendulums, I found the Period in which their Motions increased and 

 "decreased, by their mutual Action upon each other, was changed ; and would be 

 "prolonged as the Pendulums came nearer to an Equality, which from the Nature 

 "of the Action it was reasonable to expect it would." Later on we shall see that 

 there was probably an error in these observations. The continual transmissions 

 of energy and the perfectly equal rate of the clocks exclude each other to my 

 opinion. 



