356 THE CANADIAN NATURALIST. [Vol. X. 



effected by electrification; that the change of volume may under 

 certain circumstances be effected instantaneously as in flint glass, 

 or only slowly as in crown glass, and that the elastic limit of both 

 is dimished by electrification, whereas in the case of mica and 

 of gutta-percha an increase of elasticity takes place. 



Still greater strides are [being made at the present time to- 

 wards a clearer perception of the condition of matter when par- 

 ticles are left some liberty to obey individually the forces brought 

 to bear upon them. By the discharge of high tension electricity 

 through tubes containing highly rarified gases (Geissler's tubes), 

 phenomena of discharge were produced which were at once most 

 striking and suggestive. The Sprengel pump afforded a means 

 of pushing the exhaustion to limits which had formerly been 

 scarcely reached hy the imagination. At each step the condi- 

 tion of attenuated matter revealed varying properties when 

 acted upon by artificial discharge and magnetic force. The 

 radiometer of Crookes imported a new feature into these inquir- 

 ies, which at the present time occupy the attention of leading 

 physicists in all countries. 



The means usually employed to produce electrical discharge in 

 vacuum tubes was Ruhmkorff's coil; but Mr. Gassiot first suc- 

 ceeded in obtaining the phenomena by means of a galvanic bat- 

 tery of 3000 Leclanche cells. Dr. de la Rue, in conjunction 

 with his friend. Dr. Hugo Miiller,, has gone far beyond his pre- 

 decessors in the production of batteries of high potential. At 

 his lecture ''On the Phenomena of Electric Discharge," delivered 

 at the Royal Institution in January, 1881, he employed a bat- 

 tery of his invention consisting of 14,400 cells (14,832 Volts), 

 which gave a current 0*054 Ampere, and produced a discharge at 

 a distance of 0.71 inch between the terminals. During last year 

 he increased the number of cells to 15,000 (15,450 Volts), and 

 increased the current to 0-4 Ampere, or eight times that of the 

 battery he used at the Royal Institution. 



On the occasion of his lecture, Dr. de la Rue produced, in a 

 very large vacuum tube, an imitation of the Aurora Borealis; 

 and he has deduced from his experiments that the greatest bril- 

 liancy of Aurora displays must be at an altitude of from 37 to 

 38 miles — a conclusion of the highest interest, and in opposition 

 to the extravagant estimate of 281 miles at which it had been 

 previously put. 



The President of the Royal Society has made the phenomena 



