140 ANNUAL RECOED OF SCIENCE AND INDUSTRY. 



complete the circuit between circumference and centre. Un- 

 til this connection is made, the rotating disk experiences no 

 opposing force except friction. As soon, however, as the con- 

 necting arc of wive is applied, the rapid development of the 

 electrical sparks shows that the power applied to turn the disk 

 is being converted into electricity, and the power thus con- 

 sumed must be supplied by increasing the force that turns 

 tlie disk. By connecting the centre of the disk with the 

 earth, and its circumference with one plate of a condensation 

 electroscope, Le Roux has succeeded in showing that an 

 electric tension exists in the disk even when the connectino: 

 arc is not present, thus settling one of the most delicate of 

 the doubtful points in the study of induced electricity. The 

 phenomena of peripolar induction, as Le Roux denominates 

 those we have been describing, have a direct and important 

 application to terrestrial magnetism. 19 0, 1873, 102. 



BECQUEREL ON THE NATURE OF ELECTRICITY. 



Becquerel, as the conclusion of long research on the elec- 

 trical forces, says that "in the present state of our knowledge 

 of physics and chemistry, it is scarcely possible to attribute 

 to chemical affinities an electric rather than a calorific orioin. 

 What, then, is their origin ? Time will answer. They are 

 connected probably with universal ether. Let us study all 

 the causes that exert an influence upon these affinities. This 

 is the only way to effiact the removal of the veil that covers 

 this mystery." 6 i?, 1873, 851. 



ON THE NATURE OF THE ELECTRIC SPARK. 



Casin has studied the nature of the electric spark given off 

 by the Ruhmkorff induction coil, and he finds that in general 

 these sparks are complicated, although appearing to the naked 

 eye single and instantaneous. By examining such sparks by 

 means of a rapidly a-evolving perforated disk, he finds that 

 when the electrodes are small platinum bulbs, distant from 

 each other only a small fraction of a millimeter, the discharge 

 consists of hundreds of successive small sparks. When, how- 

 ever, the distance is five or six millimeters, and the electric 

 batteries are not too strong, but one bright spark is seen, so 

 that generally, as the distance of the electrodes decreases, the 

 number of successive sparks increases. 6 J^, 1873, 876. 



