Intelligence and Miscellaneous Articles, 137 



Consider now any particle of electricity in the conductor. It is 

 acted upon by the newly-discovered transverse force, tends to move 

 accordingly, and tends to draw the conductor with it. Imagine 

 enough particles of electricity crowded into the conductor, and we 

 have the explanation of the familiar action between magnets and 

 conductors bearing currents. Knowing, therefore, the strength 

 of our magnetic field, the strength of the primary current, and the 

 consequent difference of potential on opposite sides of the con- 

 ductor, we can calculate exactly the amount of electricity contained 

 in unit length of the conductor at any moment while the current is 

 flowing. Knowing, moreover, the amount of electricity passing 

 through the conductor in unit of time, which quantity is of course 

 what we call the strength of the current, it is a perfectly simple 

 matter to determine the velocity of the current. 



This question meanwhile presents itself : — If the very slight dif- 

 ference of potential existing between opposite sides of the conductor 

 is sufficient, when acting upon the electricity contained within the 

 conductor, to cause the strong action which every one has observed 

 between magnets and conductors bearing currents, why is there not 

 an enormously greater force always acting upon the conductor in 

 the direction of the primary electromotive force and primary cur- 

 rent? 



To get a more definite view of the matter, suppose we send 

 through a strip of gold leaf, a centimetre wide and of any length, a 

 current of strength '05 (cm.-grm.-sec), and place the strip in a 

 magnetic field of strength 4000. A certain difference of potential 

 would now be observed between points opposite each other on the 

 edges of the strip. This difference of potential, E', would, in the N 

 case imagined, be perhaps ^Vo" tne difference of potential, E, for 

 two points a centimetre apart in the line of the main current. Now 

 the force acting upon a unit length of the conductor to move it 

 across the lines of magnetic force would be 4000 x '05 = 200 dynes. 



This force everybody knows to exist. Let us suppose for the 

 moment, with Prof. Boltzman, that it is due to the difference of 

 potential E' acting upon the electricity in the conductor. But now 

 we have the difference of potential E, 3000 times as great as E', 

 acting upon the same electricity, but acting in the direction of the 

 current. 



To be consistent, therefore, we must look for a force in this di- 

 rection equal to 3000x200=600,000 dynes, a force equal to the 

 weight of about 600 grams, acting upon each unit length of the 

 gold-leaf strip. Thus, in following out Prof. Boltzman's assump- 

 tion to what seems to me its necessary consequences, we are led to 

 a manifest absurdity. 



Another objection to the above assumption, and a serious one 

 apparently, is found in a fact not known to Prof. Boltzman when 

 his note was written. 



The transverse electromotive force in iron is opposite in direction 

 to that in gold. According to the theory proposed, therefore, an 

 iron wire bearing a current should move across the lines of mag- 



Phil. Mag. S, 5. Vol. 10. No, 60. Aug. 1880, t L 



