On Magnetic Circuits. 335 



is the analogue of the phenomenon of hysteresis in magnetism. 

 A certain amount of the energy of the electrical discharge is 

 spent in overcoming the dielectric viscosity of the air, and in 

 straining the air dielectric. This strain is not immediately 

 released in unison with the electrical surgings. 



2. The discussion of our entire results shows unmistakably 

 that electrical oscillations in air are not represented fully by 

 the theoretical equations employed by Hertz. Since the latter 

 writer has taken the term resonance from the subject of 

 acoustics, and has given it a new significance in relation to 

 electrical waves, we are tempted to draw also an analogy from 

 the subject of sound. Laplace showed that the discrepancy 

 between the value for the velocity of sound in air calculated 

 from the theoretical equation, and that obtained by experi- 

 ment, was due to a transformation of energy in heating and 

 cooling the air during the passage of the sound wave. Our 

 experiments on the transmission of electrical waves through 

 the air show also that the values calculated from the theoretical 

 equation do not agree with the experimental values. The dis- 

 crepancy, we believe, can be explained also by a consideration 

 of the transformation of energy in the dielectric. 



3. The periodicity which we have studied is most manifest 

 when the variable capacity of the air condenser bears a suit- 

 able relation to the time of the electrical surgings. 



4. The electrical waves are apparently unaffected by passing 

 through glass which is placed in an intense magnetic field, the 

 direction of the electrical strain being perpendicular to that of 

 the magnetic strain. The displacement currents of Maxwell 

 in this case do not appear to affect the time of electrical 

 surgings. This conclusion, however, may be modified by 

 experiments which we shall try on a more extended scale. 



XXXVIII. On Magnetic Circuits. 

 By H. E. J. a. du Bois* 



A CONSIDERABLE extension of our knowledge of mag- 

 netic induction has lately taken place. This, like many 

 other additions to the realm of science, was chiefly called for 

 in order to meet the wants of designers of electric machinery; 

 and it has accordingly been arrived at in an essentially prac- 

 tical way. The aim of this preliminary communication is ta 

 show how physical science may draw advantage from some of 

 these results, and may obtain them by unobjectionable purely 



* Translation communicated by the Author,, being the abstract of a 

 paper read before the Physik. Gesellschaft, Berlin, June 27, 1800. 



2 A2 



