ELECTRON AGXETIC EFFECT OF COXYECTIOX-CURREXTS .*'>"> 



part of the room. To determine H at the sine-galvanometer a metre 

 brass circle is put around the sine-galvanometer, and the needle of the 

 latter used as the needle of the tangent-galvanometer thus made. 

 I- ing this tangent-glavanometer in connection with a Weber electro- 

 dynamometer, H at the sine-galvanometer is measured. 



The charging was by a Holtz machine connected to a battery of six 

 gallon Leyden jars. These latter are in circuit with a reversing-key, 

 an electrostatic gauge, and the disks. 



The potential was measured by a large absolute electrometer; all 

 previous observers have used spark-length between balls, with Thom- 

 son's formula. Greater accuracy is claimed for this work, largely on 

 this account. 



In this instrument the movable plate is at one end of a balance-arm, 

 from the other end of which hangs, on knife-edges, a balance-pan. 

 This movable plate is surrounded by a guard-ring. 



The lower plate is fixed by an insulating rod to a metal stem, which 

 slides up and down in guides. The distances are read off on a scale on 

 the metal stem. The zero reading is got by inserting a piece of plane 

 parallel glass whose thickness has been measured. The lower plate and 

 <riiard-ring have a diameter of 35 cm., and the movable disk a diameter 

 of 10 cm. 



The routine of the observations was as follows: A determination 

 of H and the needle-constant (/?) was first made. The electrostatic 

 gauge was then set at a certain point, and readings of difference of 

 potential were taken. The disks were now started, electrified, and a 

 series of three elongations of the needle taken; the electrification re- 

 versed and three more elongations taken, &c. 



About every five minutes speed-readings had to be noted, and at each 

 reversal it was necessary to replenish the charge in order to keep the 

 gauge-arm just at the mark. In this way a ' series ' of readings con- 

 sisting of about 25 reversals was made. After the series, electrometer 

 readings were again taken; the conditions were then changed in some 

 way. and another series begun. 



The circumstances to be changed are : distance of disks from needle ; 

 distance of glass plates from needle; electrification; and direction of 

 rotation. 



The calculation of the deflexion is based on the assumption that the 

 magnetic effect of a rotating charge is proportional to the quantity of 

 electricity passing any point per second, just as with a conduction- 

 current. Below are the formulae used. 



