654 Prof. J. Patterson on the Electrical 



straight. Before the film was deposited on the glass the 

 silvered ends were carefully polished. 



Fig. 1. 



The apparatus used in depositing the films is shown in 

 fig. 2. B consisted of a number of pieces of plate glass of such 

 a height that the glass strip D, which rested on them, was at 

 the proper distance from the cathode. C is a piece of optical 

 glass so adjusted that its surface is in the same plane as that 

 of D, while E is a cover-glass which could be shaken off 

 when the proper conditions were obtained. The cathode was 

 held in a horizontal position by means of the small rod Gr, 

 which fitted tightly into the brass tube H. All the joints 

 marked F were made air-tight with sealing-wax and were 

 very satisfactory. The glass strips were put in and taken out 

 by removing the base plate. The apparatus was connected 

 to the pump and drying-bulb with compression tubing. This 

 enabled the cover-glass E to be shaken off by tilting the jar. 

 The discharge was produced by an induction-coil with an 

 Apps' interrupter. The jar was exhausted until the strip 

 was in the negative glow and about 2 mm. from the Crookes's 

 dark space. The discharge was then allowed to pass for 

 some time and the exhaustion continued until the vacuum 

 became constant. The cover-glass was then shaken off and 

 the film deposited. It usually required from one to two 

 hours to exhaust the bell-jar and deposit the film. 



The distance of the glass strip from the cathode was usually 

 about 15 or 20 mm. This seemed to be the most satisfactory 

 distance, for if greater than this it was difficult to keep the 

 vacuum constant long enough to deposit the film without a 

 great loss <*£ time in letting the discharge pass and exhausting 



