230 Mr. G. T. Beilby. The Effects of [June 4, 



" Calculating from the ordinary conductivity of silver, a film 7 cm. 

 long x 3-5 cm. broad, having a resistance of 3 ohms, would have 

 a thickness of O'OOOOl mm. (100 /&/*)." 



Fig. 14 is a photograph of the actual film, No. 11, of the foregoing 

 report. 



Figs. 29 and 30 are photographs of the silver film, No. 14 (Bushy), 

 by transmitted and by oblique light. The vertical band on these 

 figures is the result of a needle scratch, which has uncovered the 

 glass. 



Neither in the case of the chemically deposited silver, nor in that of 

 the gold paint, was there anything to suggest such complete dis- 

 continuity as the electrical tests would lead one to expect. In the 

 gold film, especially, there appeared to be such a depth of granules in 

 the film as would, even with the most open packing, supply a 

 conductor of fair average cross-section. The under side of the film, 

 examined through the glass or mica, appeared continuous, and closely 

 adherent to its support. 



Further experiments on electrical conductivity of annealed metals 

 are now in progress. 



Dr. Glazebrook has directed my attention to papers by A. C. 

 Longden* on "Electrical Resistance of Thin Films, deposited by 

 Kathode Discharge." According to Mr. Longden, it was found that 

 thin films had a negative, while thick films had a positive temperature 

 coefficient. 



These conclusions obviously do not apply to annealing temperatures 

 used in my experiments, the increase of resistance in the Bushy tests 

 being of an altogether different order from that referred to by 

 Mr. Longden. 



When a gold leaf laid on glass by Faraday's method is exposed for 

 a very short time to mercury vapour, minute globules of mercury 

 condense on the surface and, amalgamating with the gold, form trans- 

 parent spots. This transparence quickly spreads and the whole leaf 

 becomes almost as transparent and free from metallic reflection as if 

 it had been annealed by heat. When the operation is watched with 

 the microscope the mercury is seen shooting in thin streams between 

 the plies and folds of the gold leaf. The final effect is similar to 

 that obtained by heat annealing; there is the same transparent 

 granulated film covering the glass, while the thicker brown-green 

 aggregations form a skeleton outline of the ribs and markings of the 

 leaf. Fig. 28 is a photograph near the edge of the leaf. Outside the 

 edge and on the right is the uncovered glass surface with globules of 

 mercury dotted over it. 



If the mercury -treated leaf is heated sufficiently to drive off the 

 mercury a very transparent film of annealed gold is left behind. 

 * ' Physical Review,' pp. 40 and 84 (11), 190D, and p. 355, Dec., 1902. 



