440 Mr. J. Henry on the Deflexion by Magnetic 



deflexion by magnetic force, experiments were next made to 

 see how far this connexion went. 



Details of Experiments. 



In these experiments the discharge-tube was placed between 

 the poles of a powerful electromagnet so that a very intense 

 magnetic field could be employed ; the discharge-circuit was 

 arranged in four different ways, and for each the duration 

 and the deflexion of the discharge were observed, with the 

 gas in the discharge-tube at different pressures. 



(1) The discharge -tube was connected directly with the 



terminals of the secondary of the induction-coil. 



(2) The same as (1), except that a spark-gap was made in 



one of the wires leading to the induction-coil. 



(3) The arrangement shown in fig. 13. 



(4) The same as (3), but with a spark-gap made in the 



circuit at the point marked a in the diagram (fig. 13). 

 The duration of the discharge in each case was roughly 

 estimated by the extent of the broadening of the image in a 

 rotating mirror, and the magnetic deflexion by direct obser- 

 vation. 



Results obtained. 



In case (1) the deflexion produced by the magnetic force 

 was small for high pressures of the gas in the discharge-tube, 

 but increased greatly with a considerable broadening of the 

 discharge as the pressure of the gas fell. 



The duration of the discharge also increased as the pressure 

 of the gas fell, and the broadening of the discharge, seen in 

 the rotating mirror, seemed proportional to that produced by 

 the magnetic force. For high pressures of the gas the 

 discharge seemed instantaneous. — 



(2) The external spark-gap always diminished the deflexion 

 greatly, but did not entirely destroy it, except for very high 

 pressures of the gas in the discharge-tube. The effect of the 

 spark-gap was greater the greater its length. 



The appearance of this discharge in the rotating mirror was 

 a bright line followed by a fainter band of varying breadth, 

 depending inversely on the length of the spark-gap and the 

 pressure of the gas in the discharge-tube. This fainter portion 

 of the discharge was always more deflected than the bright 

 part, and the latter was not sensibly broadened either by the 

 magnet or by the mirror. 



(3) Here the discharge for high pressures of the gas was 

 practically instantaneous ; no broadening could be seen in the 

 rotating mirror, and the magnetic deflexion vanished. The 



