1887.] 



" New Force " of M. J. Thore. 



349 



The motive force producing these rotations is, at high exhaustions, 

 the molecular impacts between adjacent surfaces of the suspended 

 cylinders excited by the radiation falling on them from the hot water, 

 hot spiral, or a candle (which is equally effective). But what pro- 

 duces the negative rotation at ordinary atmospheric pressure ? Air 

 currents are the obvious explanation, but there are grave reasons for 

 believing this explanation inadequate. In the first place actual air 

 currents when tried do not produce the desired result. Secondly, it 

 is most logical to assume that as the present set of experiments are 

 strictly parallel with those tried in 1875, and as in each case the 

 results at high exhaustions are due to molecular bombardment, so 

 also must the similar results at low exhaustions be due to the same 

 cause. 



Finally, twenty-one experiments in the form of a table are de- 

 scribed, in which an apparatus was employed, specially designed to 

 eliminate the interfering action of air currents, and submit the 

 molecular bombardment theory to crucial experiments. The results 

 are considered by the author as conclusive in favour of this expla- 

 nation . 



Addendum, May 24, 1887. 



I sent M. Thore a detailed account of my experiments, asking him 

 to favour me with any comments or remarks he might wish to make. 

 I have just received a long communication, partly printed and part 

 in MS., in which he describes many fresh experiments, and adduces 

 arguments to show that my dynamical explanation is not sufficient to 

 account for more than a few of the facts he describes, and saying that 

 he "persists in still believing that this force emanates from the 

 observer, or else that the observer is the indispensable intermediary 

 for its manifestation." 



The experiments are numerous and are devised with great inge- 

 nuity. It is impossible in the space of a brief abstract to do more 

 than refer to a few of the principal facts here brought forward. 

 M. Thore commences by objecting to my having experimented in an 

 enclosed space, saying that he always operates in free air. He thinks 

 that enclosure may almost or quite suppress his force. To this I can 

 reply that I have myself verified nearly all M. Thore's facts of rotation 

 (including those just now communicated), when working in the free 

 air of a large room, and it was only when I found the delicacy of 

 the observations was impeded by draughts and currents that I 

 put screens round the apparatus. I have not found glass screens 

 interfere materially with any of the rotations. M. Thore now says 

 that it is necessary to hold the pillar or the exciting body in contact 

 with the hand during the whole duration of the experiment. I 



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