30 REPORT — 1882. 



gases (Geissler's tubes), phenomena of discharge were produced whicli 

 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 by the imagination. At each step, the condition of 

 attenuated matter revealed varying properties, when acted upon by elec- 

 trical discharge and magnetic force. The radiometer of Crookes imported 

 a new feature into these inquiries, which at the present time occupy tho 

 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 succeeded in obtaining 

 the phenomena by means of a galvanic battery of 3,000 Leclanche cells. 

 Dr. De La Rue, in conjunction with his friend Dr. Hugo Miiller, has gone 

 far beyond his predecessors 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 battery of his own 

 invention consisting of 14,400 cells (14,832 Volts), which gave a current 

 of 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. 



With the enormous potential and perfectly steady current at his dis- 

 posal, Mr. De La Rue has been able to contribute many interesting facts 

 to the science of electricity. He has shown, for example, that the beautiful 

 phenomena of the stratified discharge in exhausted tubes are but a modi- 

 fication and a magnification of those of the electric arc at ordinary atmo- 

 spheric pressure. Photography was used in his experiments to record the 

 appearance of the discharge, so as to give a degree of precision otherwise 

 unattainable in the comparison of the phenomena. He has shown that 

 between two points the length of the spark, provided the insulation of the 

 battery is efficacious, is as the square of the number of cells employed. 

 Mr. De La Rue's expei-iments have proved that at all pressures the 

 discharge in gases is not a current in the ordinary acceptation of the 

 term, but is of the nature of a disruptive discharge. Even in an appa- 

 rently perfectly steady dischai^ge in a vacuum tube, when the strata as 

 seen in a rapidly revolving mirror are immovable, he has shown that 

 the discharge is a pulsating one ; but, of course, the period must be of a 

 very high order. 



At the Royal Institution, nn the occasion of his lecture, he pro- 

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

 and he has deduced from his experiments that the greatest brilliancy 

 of Aurora displays must be at an altitude of from thirfcy-seven to 

 thirty-eight miles — a conclusion of the highest interest, and in opposi- 

 tion to the extravagant estimate of 281 miles, at which it had been pre- 

 viously put. 



The President of the Royal Society has made the phenomena of elec- 

 trical discharge his study for several years, and resorted in his important 



