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



current of air or gas. Another French philosopher, M. Perrot, 

 afterwards discovered* that the heating power of this luminous 

 atmosphere is much greater than that of the true spark ; and at 

 the same time he found the means of completely separating the 

 atmosphere from the rest of the spark. For this purpose M. 

 Perrot opposed to one of the electrodes another of a V-shape, 

 and found that, by suitably regulating the distance of the extre- 

 mities of the latter from the former, he could establish an atmo- 

 spheric current which carried the luminous atmosphere towards 

 that branch of the V-shaped electrode which was more remote 

 from the opposite pole. Under these circumstances the lumi- 

 nous atmosphere appeared only at this latter branch, the other 

 • branch receiving the ordinary spark. About the same time 

 M. du Moncel submitted the inductive spark to the action of 

 powerful electro-magnets, and discovered that while the ordinary 

 spark is entirely unaffected by magnetic force, this luminous 

 atmosphere appears affected in precisely the same manner as the 

 voltaic arc under similar circumstances. 



2. When an ordinary Ruhmkorff's apparatus is made use of, 

 most of the phenomena I am about to mention would require to 

 be observed by means of a microscope. This, however, is not 

 the case when more powerful apparatus is employed. I have 

 recently repeated all these experiments with a machine lately 

 constructed by M. Ruhmkorff, and which produces sparks 31 

 centims. long. With this apparatus the phenomena in question 

 are produced on a scale of such magnitude as to be perfectly 

 visible to the naked eye. 



3. M. du Moncel has endeavoured, as is well known, to ex- 

 plain these phsenoniena by means of a theory which he has pro- 

 pounded in several communications to the Academy of Sciences f. 

 Unfortunately, however, this theory has not, I believe, obtained 

 the general assent of physicists ; and the same may be said of 

 other attempted explanations that have been advanced by various 

 other distinguished philosophers. There is, therefore, a want 

 here which I am about to satisfy by means of a new theory, 

 which will be seen, however, to bear some resemblance to that 

 of M. van derWilligen J. 



4. If we inquire what is the electric state of the inductive wire 

 at the moment before its discharge, it seems to me that but one 

 answer can be given : — the middle, portion is in its natural state, 

 and the two extremities arc charged, the one with positive, and 



* Comptes Rendus, vol. xlix. p. 175. 



t This theory is also advocated in a work entitled " Researches on the 

 Non-homogeneity of the Electric Spark," by Vicomte du Moncel. Paris, 

 1860. 

 • % PoggendorfPs Annalen, vol. xcviii. p. 494. 



