1897.] HOUSTON, KEXXELLY — THE PATH OF A CURRENT. 173 



electrodes, some luminous effects (as in gases), thermo-electric 

 effects broadly and of some magnetic effects. It is an estab- 

 lished fact that when a conductor carries a so-called current the 

 magnetic lines of force or flux do not exist only in the space around 

 it, but they are present also within the cross-section of the conduc- 

 tor. Their density is, however, smaller at points inside the cross- 

 section than at points immediately outside of it and at the centre of 

 a circular homogeneous cross-section this density is equal to zero. 

 Does this not clearly point to the conclusion that the action which 

 produces the field in the surrounding space has its seat in the cross 

 section of the conductor and extends throughout the same ? 



Even for effects such as those of so-called free static electricity 

 which seem clearly to have their seat at the boundary between the con- 

 ductor and the space surrounding it, can we disregard the conductor 

 which is an essential part of the apparatus, though the effects so far 

 discovered in such cases seem to reside in the surrounding space ? 



Turning now from the consideration of continuous currents to 

 that of very rapidly alternating or freely alternating currents which 

 generate waves of electromagnetic disturbance in space, as first 

 demonstrated by Hertz, we find that, on connecting the charged 

 conducting bodies, the disturbance originates on these bodies and 

 gradually spreads into space with the velocity of light. The phe 

 nomenon starts with a current having its seat on the conducting 

 bodies and the surrounding space is affected subsequently, 'as by 

 light emanating from a spark. Is it then not natural to consider the 

 conductor as the seat of the current and as the primary factor in the 

 apparatus ? 



In view of these considerations, I cannot but retain the point of 

 view stated above, though I am ready to admit that, as the changes 

 of distribution of energy take place through the surrounding space, 

 the latter may be considered as more important than the conductor. 

 It should not be forgotten, however, that we can only postulate but 

 not demonstrate the travel of energy, while we can measure its dis- 

 appearance at one point and its appearance at another. We can 

 only find changes in the distribution of energy. Now if we con- 

 sider a conducting circuit of inappreciably small resistance; a current 

 of any strength can be existent without a comparatively appreci- 

 able change in the distribution of energy, which shows that even 

 the practical importance of this action is not always evident. 



PROC. AMER. PHILOS. SOC. XXXVI. 155. M. PRINTED JULY 29, 1897. 



