Intelligence and Miscellaneous Articles, 233 



of the air for magnetic and dielectric polarization, other values of 

 this velocity of propagation will agree with the rest of the facts. 



Meanwhile a long series of experiments have now been published 

 by P. Blaserna*, from which he concludes that the propagation, at 

 least of the inducing effects of electrical currents, in the air proceeds 

 with a very moderate velocity. According to his experiments with 

 induction-discharges from open circuits (which he considers the most 

 reliable), this velocity in air amounts to only 550 metres, in gum-lac 

 to not more than 330 metres, and is consequently, in the latter case, 

 about equal to the velocity of sound in air. From his experiments 

 with a closed induction circuit he deduced much smaller velocities ; 

 yet he has himself acknowledged that the reaction of the induced 

 upon the inducing spiral made the interpretation of the result of bis 

 experiments doubtful. 



It is to be remarked that in these experiments the distances be- 

 tween the inducing and the induced spiral were very small, varying 

 between 1 and 3 centims. ; besides, the two spirals were wound flat. 

 The time corresponding to the propagation through the interval of 

 2 centims. amounted, in the experiments with open induction, to 

 only -g- 2u ou 0I " a second. Neglecting the irregularities occasioned 

 in delicate measurements of time, by the contact between solid me- 

 tals being always broken by successive leaps, it appeared to me 

 doubtful whether such minute differences of time might not be con- 

 ditional on the variable duration of the spark at the place of inter- 

 ruption of the inducing current. In my experiments hereinafter 

 described, I convinced myself that, even in much more unfavourable 

 conditions than were present in M. Blaserna's experiments, the in- 

 terruption-spark may have a duration of xtroxnr 0I " a second ; MM. 

 Lucas and Cazin recently found 3-jy-JnHf f° r larger electrical batteries 

 with 2*292 millims. striking- distance, y 5 o ou with 5 millims. striking- 

 distance t> While M. Blaserna employed several Bunsen's elements 

 for the production of the current, I used only one Daniell's element ; 

 and while his spirals contained close-pressed coils of wire, mine had 

 a very large periphery and few coils, and was therefore much less 

 calculated to produce a strong extra-current ; and yet the duration 

 of the spark reached the quantity stated. Now, when we consider 

 that, as is well known, the approach of a second spiral, in which an 

 induction-current is produced, seriously diminishes the intensity of 

 the spark, because the induced current counteracts the inducing, 

 and that M. Blaserna's spirals were always proportionally very near 

 each other, the doubt occurs whether the longer duration of the 

 spark did not produce an apparent retardation of the operation with 

 a greater distance of the spirals. 



As I had for a long time been occupied with experiments on the 

 course of electric currents of very short duration, and had had appa- 

 ratus manufactured for this purpose, it seemed to me before all things 

 necessary to prove whether the velocity of propagation of electrody- 

 namic effects has really so low a value as M. Blaserna has concluded. 



* Giornale di Scienze Naturale ed Economiche, vol. vi. 1870. Palermo. 

 t M. J. Bernstein, in a close-coiled spiral of fine wire, 2 o"o (Poggen- 

 dorff's Annalen, vol. cxlii. p. 65). 



