Resistance of Thin Metallic Films. 469 



2*5 cm. square, was fixed in a wide glass tube 4*5 cm. in 

 diameter, which could be exhausted by means of an automatic 

 pump. The top of the cathode was covered with mica. The 

 anode A passed down through the centre of a tap (the purpose 

 of which will presently be described) and was fixed perma- 

 nently in position in the wide tube. The ends of the apparatus 

 could be closed with glass plates B and D cemented on with 

 sealing-wax. 



A plate 1*5 cm. wide and 3*5 cm. long was taken, and a 

 piece of tinfoil 2*5 mm. wide having been placed along the 

 centre line parallel to the length of the plate, the whole of 

 the remainder was covered with a thick deposit of platinum. 

 On removing the tinfoil a clear space was left across which 

 the films to be examined were afterwards deposited in different 

 positions. To this end the plate was arranged to slide 

 parallel to the axis of the tube, in a frame provided with two 

 glass guides. One end of the plate was attached to a thread 

 which passed through two eyes cemented to the plate D. 

 The other end of the thread was attached to the tap, so that 

 by turning the latter the plate could be slid along under the 

 cathode. A piece of mica was fixed to the framework so as 

 to completely cover the plate without touching it, and the 

 films were deposited through a slit cut in this mica perpen- 

 dicular to the axis of the plate, and extending right across 

 the thick platinum strips. 



About 10 films of different thicknesses were deposited. 

 The plate was then removed, aud after slits had been cut in 

 the platinized strip on one side of the plate, so as to separate 

 the films, the latter presented the appearance shown in 

 fig. 1, M. As a precaution against accidental short-circuiting 

 along the edge of the plate, the whole of the platinum was 

 cleared away to a distance of 1 mm. from the edge. In 

 order to allow of connexion being made to the various films, 

 a set of tongues corresponding to the separate sections of 

 the strip was cut in a piece of copper foil (see N, fig. 1). 

 These were gripped firmly in position by means of a spring- 

 clip provided with cork-lined jaws to ensure a tight contact, 

 and after snipping the foil along the position indicated by 

 the dotted line, wires were soldered to each oi: the tongues. 

 A piece of foil with a wire attached was also gripped to the 

 strip G. The whole arrangement was put in a glass tube 

 3 cm. in diameter and plugged in with cotton wool, the tube 

 being afterwards corked at the top while the wires passed 

 out through the cork. 



The films were deposited by the discharge from a 4-inch 

 coil, the interrupter being adjusted to run very steadily. 



