334 On Electrical Oscillations in Air. 



Boltzman"* and Klemencin f have experimented on the 

 specific inductive capacity of gases and vapours, and it is seen 

 from their results that the agreement between the square root 

 of the capacities of the simple gases and //,, the index of re- 

 fraction for light of these gases, is quite close, as is demanded 

 by Maxwell's electromagnetic theory of light. A marked 

 difference, however, was found to exist in the case of more 

 complicated molecules — sulphurous acid, or ethyl bromide, for 

 instance. It is probable that the changes of specific capacity 

 of heterogeneous media under rapidly alternating forces con- 

 stitute an important factor in considering the possible agree- 

 ment between Maxwell's theory of light and the results of 

 experiment. 



In order to see if an intense magnetic field could modify 

 the transmission of electrical waves through a dielectric, the 

 following experiment was tried. A glass Leyden-jar, 2*5 

 centim. in diameter and 28 centim. in height, connected with 

 our inductance-circuit, was placed inside a coil consisting of 

 728 windings of large wire. The outer and inner radii of 

 this coil were 27*7 centim. and 34 centim. Its height was 

 40*5 centim. The magnetic field in this coil was supplied by 

 a Gramme machine, which gave a current through the coil of 

 approximately 30 amperes. It was expected that a certain 

 amount of the energy spent in producing the electrical waves 

 would be consumed in a reaction on the magnetic field. The 

 total duration of the electrical discharge did not appear to 

 be notably affected by the magnetic field. Certain experi- 

 ments seemed to show a decrease in the total number of 

 electrical oscillations. A large number of experiments will 

 be necessary to decide upon the effect of a magnetic field upon 

 the passage of electrical waves through a dielectric. The 

 difficulty of obtaining an electrical discharge under the same 

 difference of potential made the experiment an extremely 

 difficult one. The method seems to us to promise a discovery 

 of Maxwell's displacement currents in dielectrics ; and we are 

 therefore continuing our researches in this direction with a 

 modified form of apparatus. 



Conclusion. 



1. The electrical oscillations in the air between the plates of 

 an air condenser show a periodicity extending through the 

 entire range of oscillations. We believe that this periodicity 



* Pogg. Ann. cli. p. 403 (1875). 



t Abstract of Journal of the Society of Telegraph Engineers (1886), 

 p. 108. 



