Number of Electrostatic Units in the Electromagnetic Unit. 431 



Does not the " rotatory coefficient " of resistance completely 

 express the important facts discovered by Mr. Hall ? Instead 

 of expressing these facts by saying that there is a direct action 

 of a magnetic field on a steady current as distinguished from 

 the body conducting the current, may we not with equal con- 

 venience express them by saying that the effect of a magnetic 

 field on a conductor is to change its coefficients of resistance 

 in such wise that the electromotive force is no longer a self- 

 conjug ate-line&r-Yector function of the current ? 



L. On the Number of Electrostatic Units in the Electromagnetic 

 Unit. By R. Shida, M.E. y Imperial College of Engineer- 

 ing y Tokio, Japan*. 



THE object of this paper is to explain measurements made 

 during the month of July last for an evaluation of " v" 

 the number of electrostatic units in the electromagnetic unit 

 — a question which has much engaged the attention of the 

 British Association. We can evaluate " v " by determining 

 the electrostatic and also the electromagnetic measure of any 

 one of the following terms — Electromotive Force, Resistance, 

 Current, Quantity, and Capacity. It is the first of these terms 

 that I measured in the two systems of units; and the E.M.F. 

 was that of Sir William Thomson's gravity Daniell, which is 

 very constant. The question divides itself into two parts : — 



(A) Absolute Electrostatic Measurement of the E.M.F. 



This measurement was made by means of Sir William 

 Thomson's absolute electrometer. It is not easy to explain 

 shortly how the electrostatic measurement is made by this 

 instrument ; but, briefly speaking, it is as follows : — Imagine 

 a circular disk suspended by springs in a horizontal plane 

 inside the aperture of another larger plate in the same plane, 

 with a continuous plate below and parallel to them. The force 

 of electrical attraction of the continuous plate on the disk is 

 compared with the gravitating force of a known weight. To 

 effect this, any electrical influence having been entirely re- 

 moved, a known weight is put on the disk, which is then 

 raised by means of a micrometer-screw until it comes to its 

 original position ; and then the weight is taken away, allow- 

 ing electrical force to act when the continuous plate is adjusted 

 by the aid of another micrometer-screw, to bring the disk to 

 the same position as before. A full account of the instrument 

 will be found in Sir William Thomson's Report on Electro- 



* Communicated by Sir William Thomson, having been read in Sec- 

 tion A of the Meeting- of the British Association at Swansea. 



