DR. HAROLD A. WILSON ON THE ELECTRIC EFFECT OF 



The end JJ of the solenoid was closed by two semi-circular brass plates screwed on 

 as shown. These served to screen off electrostatic effects due to the driving belt 

 charging up. The inside surface of the solenoid was kept cool by means of the water 

 jacket WWWW, through which a rapid stream of tap water was always kept 

 flowing when the apparatus was in use. The water was made to flow in a spiral 

 path round the solenoid by means of a spiral partition inside the jacket. 



The solenoid was wound on a brass bobbin in two sections, and the windings were 

 carefully insulated from the bobbin. A current of 15 amperes could be passed for 

 some time through the solenoid, using a P.D. of about 50 volts, without undue 

 heating. 



The cylinder was driven by a leather belt 2 centims. wide and - :5 centim. thick, 

 with a very well made splice. The belt was driven by a half horse- power continuous, 

 current motor which ran at about 1450 revolutions per minute with 50 volts. Three 

 driving pulleys were used, 10 inches, 5 inches, and 2^ inches respectively in diameter. 

 The pulley on the cylinder shaft was l inches in diameter, so that speeds of about 

 11,600, 5800 and 2900 revolutions per minute could be obtained. 



The arrangement of the apparatus is shown in fig. 4. The number of revolutions 



P n 



B 



M 



Fig. 4. AA, tubes taking oil to hearings ; BBB, driving belt ; CCC, metal screen round insulated wire ; 

 E, quadrant electrometer; M, i-H.P. motor; 0, oil reservoir; PP, motor pulley; SS, solenoid; 

 T, electrometer table ; WW, insulated wire ; Y, mercury cup ; Z, guard-ring condenser. 



made by the cylinder could be registered on a small speed counter. A brass disk 

 FF (fig. I), having a screw thread cut on its circumference, was screwed on to the 

 driving pulley. The screw thread geared into a cog-wheel with 100 teeth carried on 

 the axle of a ' Veeder ' revolution counter, indicating from to 99,999 revolutions. 



