302 
PHYSICS: P. W. BRIDGMAN 
Proc. N. A. S. 
Current Density, 106 Amp/cm2. 
FIG. 3 
The form of the curve is not that supposed as a first approximation by 
Maxwell, but the departure rises more rapidly than the square of the cur- 
rent. In fact the form of the curves seems to suggest infinitely high 
order of contact with axis at the origin. If however, for the purpose of 
numerical comparison we assume that below current densities of 10 6 amp./ 
cm 2 , the departure from Ohm's law is proportional to the square of the cur- 
rent within the limits of error, than the curve for thin gold shows that 
for it the resistance at 1 amp. /cm 2 , cannot differ by more than 1 part in 10 16 
from the resistance at infinitely small density (against 1 part in 10 12 of 
Maxwell). 
Theoretically the existence of this effect at currents of the order of 10 6 
amp. /cm 2 , means that, granted a free path mechanism of conduction at 
all, the free path must be much longer than supposed on the classical 
basis, and accordingly the number of free electrons much less. Now on 
other grounds I have been led to the belief that conduction is by means of a 
free path mechanism, 2 of a different sort than that supposed in the clas- 
sical theory, and that the number of electrons is much less and their paths 
longer than according to that theory. These new results are now in 
accord with this point of view. I have not been able as yet to carry through 
a more exact discussion on the free path basis and to obtain the numerical 
value for the length of the free path which these results would involve. 
The difference in results for gold of different thickness is also what would 
be expected. The results for thick gold are not nearly as accurate as for 
the thinner, but there can seem no question but that the departure is 
