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 A B 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 A B 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 AT 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 e>ach 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 ilf, 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 
