Dr. P. L. Eijke on the Inductive Spark. 445 



9. If the want of homogeneity of the inductive spark be really 

 due to the cause to which I attribute it, then it ought to be pos- 

 sible to discharge ordinary friction electricity so as to exhibit 

 both the point of light and the luminous atmosphere ; and the 

 discharge so modified, when submitted to the action of external 

 agents, ought to behave similarly to the spark produced by 

 Ruhmkorff's apparatus. It will easily be understood that I 

 attached great importance to the success of this experiment, 

 which may be considered as the touchstone of my theory. The 

 way I contrived it was as follows : — The conductor of a hydro- 

 electric machine, the grate of which possessed a surface of 9 

 square decimetres, was put in metallic connexion with the inte- 

 rior of a Leyden jar, the external coating of which presented a 

 surface of 738 square centimetres, and was in communication 

 with the boiler of the machine. The knob of the jar was also 

 connected by means of a wet hempen cord, 5 millims. in dia- 

 meter and 45 centims. long, with an insulated metallic sphere 

 of 29 centims. in diameter. The two branches of a Henley's 

 discharging rod constituted the two electrodes. The end of one 

 of them was in connexion with the external covering of the jar, 

 that of the other was at the distance of about 10 millims. from 

 the metallic sphere. The other two extremities of the two 

 branches, which were pointed, were about 7 or 8 millims. apart. 

 It is evident that, with this arrangement of the apparatus, the 

 Leyden jar ought to be discharged whenever the tension of the 

 electricity in the sphere attains a certain amount, and that this 

 discharge ought to appear as a luminous spark between the 

 pointed extremities of the discharging rod. 



The electricity which thus passes between these two electrodes 

 proceeds from two different sources, viz. from the sphere, and 

 the interior of the jar. The electricity of the sphere having but 

 a short metallic path to traverse, ought to give rise to the appear- 

 ance of an ordinary spark; while, on the contrary, the fluid 

 accumulated in the jar having to overcome the very considerable 

 resistance of the hempen cord, ought to give rise to the appear- 

 ance of a luminous atmosphere. Now the discharge actually 

 observed presents precisely this double appearance. 



10. On submitting the luminous discharge of this apparatus to 

 the action of an air-current, I obtained precisely the same results 

 as those observed by M. du Moncel in the case of the inductive 

 spark, — the luminous atmosphere being carried away from the 

 point of light, on which the air-current did not seem to exercise 

 the slightest effect. M. Perrot's experiment also succeeded per- 

 fectly. Finally, I examined the nature of the action of magnetic 

 force on the discharge, and I found that the luminous atmo- 

 sphere under the action of an electro-magnet behaved precisely 

 as in the experiments of M. du Moncel. 



