608 
126 ue to obtain definite results for the temperature-coefficient of 
the resistance; for two different specimens within the temperature 
range from 22° to 140° C. values of 0.00276 and 0.00244 respect- 
ively were found; as mentioned above the platinum wire from 
which the films were formed by evaporation has a temperature- 
coefficient of 0.005905. 
Very thin films on the other hand behaved in an entirely different 
manner: as long as they remained at room-temperature, only a very 
small change of the resistance with the time was observed and 
even with the thinnest films no deviation from Oma's law could be 
established ') (the applied voltage varied from 0.1 of a volt to 60 volts). 
When these very thin films were heated, however, (to 130°), the 
resistance was found to increase rapidly and ultimately beeame in- 
finite; the black appearance of the film does not thereby undergo 
any change. If the heating is stopped before the resistance has 
become infinite, the resistance after cooling has become much higher 
than before the heating, and moreover for a film in that condition 
Oum’s law was found to be no longer valid; with an applied voltage 
of 1 Volt a resistance is found which is 2.4 times as high as with 
a potential difference of 60 Volts. In order to ascertain whether the 
nature of the glass might possibly be the cause of the phenomena, 
we have deposited the film on lead glass as well as on potassium- 
sodium glass, but in both cases found the same phenomenon. 
A further phenomenon which was also observed with very thin 
films was as follows: a platinum film, about 3.5 uu thick, gave on 
repeated measurement a constant value for the resistance of 3.72 >< 
10* Onns; after the glass cylinder being opened by which the air 
was admitted the resistance assumed a constant value of 3.15 10* 
Ohms. This observation perhaps indicates, that the presence of air 
or possibly of moisture might play a part in the change of the 
resistance of thin films with the time. 
It is a great pleasure to us to express here also our thanks to 
Dr. G. L. F. Pamirs w. i. for his very great interest and support 
in connection with our investigation. We also wish to thank Mr. 
M. P. pe Lance who has assisted us with great assiduity. 
Eindhoven. Physical Laboratory of the N. V. Philips- 
Incandescent-lamp-factories. 
1) This result is not in accordance with Swann’s theory mentioned above. 
