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IOWA ACADEMY OF SCIENCE 
found that the same ratio does not exist between volts and amperes in the 
two instances. The current is larger after the maximum voltage has been 
applied. Pierce describes it as a slow building up of the current. In a later 
paper he quotes Braun on (Phys. Rev. 29, p. 478, 1909) the subject, in 
part as follows: “I obtained in general the phenomena that the cur- 
25 p. 36, 1907) first voltages increasing step by step, are applied to car- 
rent strength was different for different directions of the current; and 
that this difference increased with increase of the current, and then on 
keeping the circuit closed, the current for that direction in which the 
resistance was smaller increased, while for the opposite direction it 
decreased. ’ ’ 
With selenium the usual occurrence is for the resistance to decrease 
with the time of flow of the current but this is not always true. In a 
former paper (Phys. Rev. 33, p. 21, 1911) I gave results which showed 
first an increase followed by a decrease of resistance for a high voltage. 
This held only with the selenium in the Giltay cell. 
THE EFFECT OF AMALGAMATION. 
It was first observed by Moss (Proc. Roy. Soc. XXV, p. 22, 1876, and 
Nature 77 p. 198, 1908) that mercury decreases the resistance of sele- 
nium in a rather peculiar manner. A small amount of mercury accord- 
ing to him forms a film over the crystals of the selenium and renders 
the cell thereby quite conducting. More recently Minchin contended 
with the same effect under other circumstances. A certain selenium cell 
had a resistance of 61xl0 6 ohms in the dark at atmospheric pressure. 
(Nature, 77 p. 222, 1908.) In a vacuum with a partial pressure of mer- 
cury vapor the resistance fell to 17.5 ohms in 12 hours. " More recently 
the author has outlined the extent and the (Phys. Rev. Ser. 2, Vol. 2, 
p. 153) probable nature of the action of mercury vapor on selenium. 
However the important feature in this connection is the remarkable in- 
crease of the conductivity, and the light-negative characteristics called 
forth by the mercury. 
Likewise if amalgamated surfaces are brought in contact with certain 
crystals the contact resistance of the crystal disappears almost entirely, 
and only the resistance of the crystal itself may remain. Streintz and 
Wellik* call attention to a magnetite crystal which had a resistance of 
0.17 ohms under a pressure of 3000 gms when the contacts were of gold. 
The resistance of this specimen fell by using gold-amalgam contacts from 
0.17 to 0.008 ohms. This result is also typical of what is obtained by 
*Phys. Zeits, 12 p. 845, 1911. 
