Mr Wilson, On the Magnetic Deflection of Cathode Rays. 181 



The apparatus used is shown in the accompanying figure. 

 KNC is a glass tube 2 cms. in diameter and about 20 cms. long. 

 At C a conical bulb CD is blown 20 cms. long and 10 cms. in 

 diameter. A tube AB was sealed on across the tube KNC and 

 served to contain the cathodes of different metals. 



The cathodes were each 1 cm. square and were fastened to 

 the under side of a strip of mica 1 cm. wide and 10 long. They 

 were fixed about 2 mms. apart. At one end of the strip a piece of 

 thin sheet iron was fastened on by means of which and a small 

 electromagnet the mica and cathodes could be moved along the 

 tube AB so that any desired cathode could be brought over the 

 tube NC. 



Connection with the particular cathode to be used could be 

 made by means of an aluminium wire fixed in a glass tube and 

 suspended from the electrode if by a spiral spring S. A small 

 cylinder of soft iron was fixed round this wire near its upper end 

 which enabled it to be raised off the cathodes by means of an 

 electromagnet. 



A small hole was made in the mica strip, above each cathode, 

 in which the aluminium wire rested and made contact with the 

 upper side of the cathode. 



Thus to change from one cathode to another it was merely 

 necessary to first raise the aluminium wire and then slide the 

 mica along until the desired cathode was in position when the 

 wire could be lowered again. 



The cathode rays passed down the tube NC and through a 

 small hole in an aluminium diaphragm at C which allowed a 

 narrow beam to enter the bulb CD. This beam produced a fluor- 

 escent spot on the glass at D by means of which its position 

 was known. The anode was an aluminium wire in the side 

 tube H. 



The discharge was produced by an induction coil E and the 

 potential difference was estimated by means of a spark gap G 

 which was adjusted until a discharge passed both at G and in the 

 tube. 



The coil used to produce the magnetic field is shown at M, M; 

 the current in it was always of the same strength in all the ex- 

 periments. 



The deflection of the fluorescent spot at D when the current 

 in the coil was reversed was measured with a millimetre scale 

 at D. 



Cathodes of aluminium, iron, copper, zinc, tin, silver, lead, and 

 platinum were fixed on the mica strip. 



The following table contains all the observations made with 

 this tube. 



14—2 



