174 HOUSTON, KEXNELLY — THE PATH OF A CURRENT. [Mar. 19, 



Dr. a. Macfarlane : I wish first of all to express my sense of 

 'the admirable manner in which the authors have carried out the 

 aim which they set before themselves. Behind their descrip- 

 tion of the manner in which an electric current is now believed to 

 be transmitted there is a great amount of mathematical analysis 

 and experimental verification. 



In a work on the Applications of Electricity, written by Count du 

 Moncel before the beginning of the great industrial development 

 of electricity, he refers to a fanciful plan of a M. Charles Bourseul 

 for transmitting speech by electricity. The Count makes great fun 

 of the idea ; yet he lived to write a book on the telephone. What 

 struck him as especially absurd was that vibrations produced by 

 the human voice could be thought capable of transmission through 

 a solid wire of copper. And indeed it is wonderful how electri- 

 cians have been so long content to regard the current of electricity 

 as transmitted by the copper molecules, or even by the ether in the 

 wire between the molecules. 



In the study of electrotechnics there is nothing more important 

 than clear ideas about the relation of the electric current to the 

 associated magnetic flux. It is important to observe that there are 

 many analogies between the two ; but it is also important to observe 

 that the analogy is not complete. The electric current involves in 

 its idea the element of time in a way that the magnetic flux does 

 not. Now observe how the theory expounded explains this. We 

 have the complementary ideas of electric flux and of magnetic flux 

 and also the other two ideas of rush of electric flux and rush of 

 magnetic flux ; the electric current in general meaning motion of 

 the combined flux. 



For some time it was customary to neglect the study of static 

 electricity because its connection with current electricity was not 

 evident. But observe that the one idea — electric flux — comes from 

 the old science of static electricity, and the other idea — magnetic 

 flux — from the old science of magnetism : together they explain 

 the phenomena of the flow of electricity along a conductor. 



In the text-book of Electricity and Magnetism which I studied 

 there was an article headed " Velocity of Electricity." Account 

 was given of some experiments made to determine the time required 

 for the transmission of signals along conducting lines; the dis- 

 agreement of the values obtained was pointed out, and the writer 

 concluded that properly speaking there was no such thing as the 



