during the Absorption of Electrons by Platinum. 179 



whole was in a cylindrical brass box B connected through a 

 side tube with a McLeod gauge an J Gaede pump. The 

 supports of the grid and filament were fixed air-tight with 

 sealing-wax through four tubes in a glass stopper A which 

 was ground to fit a conical hole in the top of the brass box. 

 This was found to make a perfectly satisfactory air-tight 

 joint if the two surfaces were carefully ground and suitably 

 greased. The glass tubes DD supported a glass framework 

 on which the strip S was wound in the manner shown. By 

 twisting the glass rods which formed the framework very 

 quickly while they were being drawn out it was found 

 possible to produce a thread on them in which the strip could 

 be laid, and which prevented the possibility of its slipping 

 about after it had been w T ound. The return end T of the 

 strip was prevented from touching the intermediate portions 

 by being wound around two glass projections as shown. The 

 ends of the strip were soldered onto two platinum wires 

 sealed through the tubes, which were filled with mercury, and 

 thus made contact with the outside. 



The osmium filaments F were soldered onto the outside of 

 two bent brass tubes which were clamped together by two 

 glass plates K, bolted at L. The inner side of the brass tube 

 was cut and opened out as shown in section below. The 

 outer tubes were made so as to just slide on the brass rods C. 

 This arrangement carrying the filaments was placed around 

 the closed framework carrying the strip and slid onto the 

 brass rods C, being fixed in position by the screws H. It 

 w r as adjusted so that the two filaments F were opposite the 

 middle of the grid $. The object of~the Inner tubes G was 

 to shield the glass supports so that the electrons did not flow 

 onto them. It was thought that if this happened some of 

 the heating effect might be lost. 



§ 3. Method of taking Observations. 



In taking the observations it was found necessary first of 

 all to wait for a considerable length of time for the tempera- 

 ture of the system to become steady. This was usually a 

 matter of two or three hours after the heating current 

 had been turned on. Up to that time the resistance of 

 the strip S gradually increased. In fact, it was generally 

 found that no matter how long one waited there was a slow 

 drift in the direction of increasing temperature and in any 

 case there were apt to be small slow alterations one way 

 or the other. After the lapse of an hour or two, however, 

 they w r ould be so small as to be of no serious consequence 



N2 



