660 



Prof. J. Patterson on the Electrical 



copper electrolytically on the silver and copper wire to ensure 

 good contact. This precaution was found to be unnecessary 

 unless the films were to be heated or coated with paraffin. 

 The electrodes represented in figs. 8 and 9 were also used. 



Fi". 8. 



Fisr. 9. 



nW<m — 



Longitudinal Section. 



End View. 



Fig. 8 represents a longitudinal section through the elec- 

 trodes, and fig. 9 an end view of one of them. A and A' 

 were copper plates with plane surfaces and carefully polished. 

 The glass strip was tightly clamped between the plates by 

 means of the screw B. These electrodes were very satis- 

 factory, but they could not be used if the films had to be 

 placed in oil or paraffin. Another form of electrode that 

 could be used to advantage if the films were to be used as 

 standards of resistance would be a rectangular metal cap, 

 made so as to leave about a millimetre space around the glass 

 strip, and fill this space with fusible metal. This form would 

 ensure the best of contact, and, moreover, would be very 

 strong. 



Resistance of Bismuth Films. 



The bismuth cathode from which the films were made was 

 cast from the best commercial bismuth obtainable. The 

 surface of the cathode was very carefully polished and scraped 

 from time to time with a steel tool. A piece of mica was put 

 on the back of the cathode. This seemed to make the film 

 deposit faster, and also prevented the top of the jar and sides 

 from getting covered with the deposit as quickly as they 

 otherwise would. 



The results obtained for a number of films are given in 

 Table II. There appears to be an increase of specific re- 

 sistance for the thicker films, but this was due to the surfaces 

 losing their metallic lustre and becoming dull and powdery 

 in appearance. On this account it was impossible to make 

 bismuth films thicker than about 10 ~ 3 cm. 



The resistance of the films gradually increased with 

 the time, as is seen from the examples of three films 

 (Table III.) whose resistances were measured every day for 



