601 
wire was measured at the end of the experiments for tungsten and 
platinum also; the result agreed to within 2°/, with the loss of 
weight as derived from the above calculations. As the wire D is made 
much longer than the distance between the silvered rings, the quan- 
tity of metal deposited between the two rings may with near approx- 
imation be assumed to be equal to the total quantity evaporated 
from a piece of the wire equal in length to the distance of the rings. 
Measurement of the resistance of the films. 
The wire was heated at constant temperature during a given 
time, the resistance of film formed was then measured (the thick- 
ness of which as shown above is to be calculated from the velocity 
of evaporation), the wire was then heated again for a given time, 
the resistance of the film which had now increased in thickness 
was measured, etc. 
Proceeding in this manner possible changes of the resistance of 
the films with time are eliminated, seeing that the thickness of the 
film is made greater by evaporation, as soon as the resistance-measu- 
rement is finished, and that the change of the resistance in the 
course of an experiment was inappreciable. 
For the thinnest films the resistance was determined by measu- 
ring the current which is transmitted at a known voltage, by 
means of a sensitive galvanometer. For films of smaller resistance 
Wueartstone’s bridge was used and for those of the smallest resistance, 
where it becomes necessary to eliminate the influence of the leading- 
in wires, KonrrauscH’s method of the overlapping shunts was used. 
In order to be able to deduce the specific resistance from the 
measured resistances, the distance between the silvered rings and 
the internal diameter of the glass cylinder was also measured. 
Results. 
The measurements were made at a temperature of about 22° C. 
The first column of Table I contains the thickness d in uu of 
the film, the second the measured resistances 1” in Ohms and the 
third the specific resistance 6 expressed in Ohms per em/em?. 
Figure 2 gives a graphical representation of a part of the results 
given in the table. 
The value given in brackets of the specific resistance for a thick- 
ness —= op was not measured by us, but is the value which is gene- 
rally given as the specific resistance of pure platinum. 
