70 Notes concerning the Phenomena 



in apology, that while what he had to advance in this paper 

 was but a mere fragmentary contribution, he was not with- 

 out hope, leisure permitting, of prosecuting the inquiry by 

 further experiment. 



A resume of the earlier phases of the inquiry was then 

 given and the experiments of the Rev. A. Bennet * were 

 quoted : Mr. Bennet having been the first, as far as known, , 

 to record the fact that a light substance delicately suspended 

 in air moved towards warm bodies. 



The author then passed to the modern phases of the 

 inquiry, as represented by the investigations of Messrs. 

 Crookes and Reynolds. Mr. Crookes characterises the 

 results of the earlier workers as collectively unsatisfactory 

 and contradictory, and then proceeds to carry out a very 

 large number of most delicate and ingenious experiments 

 with the assistance of all the refinements of modern science. 

 His apparatus in its simplest form consists of a light stem of 

 glass with pith-ball extremities, delicately suspended hori- 

 zontally within a glass globe. When a ray of heat or light 

 is allowed to fall on one of the balls, that ball swings 

 towards the source of heat or light. When, however, the 

 globe is exhausted of air and the ray again directed on to 

 the ball, the ball then swings away from the source of the 

 ray. Before the exhaustion is complete, when the vacuum 

 gauge is within about half an inch of the barometer, a 

 neutral point is reached at which the balls remain inert 

 under the influence of these rays. 



The refinements and ingenious devices introduced by 

 Mr. Crookes into the method of conducting this fundamental 

 experiment were dwelt upon at considerable length, and his 

 application of the chemical vacuum prepared by the method 

 of Dr. Andrews fully described.f 



After most elaborate experiment, Mr. Crookes expresses. 

 his views as to the causation of these phenomena in the 

 following terms : — " My own impression is that the repulsion 

 accompanying radiation, is directly due to the impact of the 

 waves upon the surface of the moving mass, and not 

 secondarily through the intervention of air-currents,, 

 electricity, or evaporation and condensation." (Philos. Mag. 

 vol. xlviii. p. 94.) 



The experiments and views of Professor Reynolds J were 

 next entered upon, this physicist referring the cause of these 



* Chem. News, vol. xxxi. p. 1. + Ibid. p. 33. 



\ Philos. Mag., vol. xlviii. p. 146. 



