444 Dr. P. L. Rijke on the Inductive Spark. 



which resist the effect of the ordinary spark : thus, for example, 

 gunpowder can be exploded by the spark of a Ley den jar, if the 

 electric fluid is first passed through a wet cord. Now these are 

 precisely the characteristics that have been recognized as existing 

 in the luminous atmosphere of the inductive spark. 



6. According to the theory here advanced, we ought to be able 

 to augment the luminous atmosphere at the expense of the true 

 spark, and, conversely, the spark at the expense of the atmosphere, 

 as follows : — 



7. In order to increase the spark at the expense of the lumi- 

 nous atmosphere, all that is necessary is to unite each extremity 

 of the inductive wire to the armatures of a Leyden jar by means 

 of metallic conductors, and to pass the charge through a Henley's 

 discharging rod, which has one extremity of one of its branches 

 communicating with the knob of the jar, and one extremity of 

 its other branch connected with the external coating, the spark 

 passing between the other two ends of its two branches. Thi3, 

 it will be seen, is precisely the experiment of Messrs. Masson 

 and Grove. It is evident that when the two extremities of the 

 secondary wire communicate with the armatures of a Leyden jar, 

 the distribution of the electric fluid in the wire undergoes a very 

 great alteration, since, before the actual passage of the charge, 

 the greater part of the two fluids will have accumulated in the 

 armatures of the jar, whence it must result that, the two fluids 

 having now to traverse conductors offering little resistance, the 

 discharge ought to take the form of an ordinary spark; and this 

 is found to be the case. M. du Moncel has himself acknowledged 

 that, under these circumstances, the luminous atmosphere no 

 longer makes its appearance. My theory, then, not only accounts 

 for this disappearance of the luminous atmosphere, but it also 

 explains why, in the experiment of MM. Masson and Du Moncel, 

 the brilliancy of the spark is so greatly increased. 



8. When, on the other hand, we wish to get rid of the point 

 of light and to retain the atmosphere, all we have to do, accord- 

 ing to my theory, is to compel the electricity distributed through- 

 out the secondary wire to traverse a path in which it finds con- 

 siderable resistance. This I effected as follows : — For my elec- 

 trodes I took two brass wires about 1 millim. in diameter, and 

 3 or 4 centimetres long, and having fixed them to insulators, I 

 united them to the extremities of the inductive wire by means of 

 two wet hempen cords, about 5 millims. in diameter and 0*7 

 metre long. The inducing current was then produced by means 

 of two elements of a Bunsen ; s battery. Under these circum- 

 stances the ordinary spark was no longer visible, the luminous 

 atmosphere alone remained, and the whole of it would be dis- 

 placed by means of a current of air. 



