328 
PROFESSOR W. &. ADAMS AND MR. R. E. DAY ON THE 
Conclusions . — From these experiments, made with different pieces of selenium, we 
may draw the following inferences : — 
(1) That, on the whole, there is a general diminution of resistance as the battery- 
power is increased. 
(2) That the first current sent through the selenium causes a more or less permanent 
“ set ” of the molecules, in consequence of which the passage of the current, during the 
remainder of the experiments, is more resisted in that direction than it is in the oppo- 
site one. 
(3) That the passage of the current in any direction, at any period of the series of 
observations, produces a slight “ set ” of the molecules, which tends to facilitate the 
subsequent passage of a current in the opposite, but obstructs one in the same direction. 
Hence, when the current is sent through the selenium twice successively in the same 
direction, the resistance observed in the second case, even with the higher battery-power, 
is often equal to, or greater than, what it was in the first. 
In some cases (for example, in the first of the series of observations wdth No. 10, see 
page 325) the first value of the resistance was less than one taken immediately afterwards 
with the current in the opposite direction. In these cases, however, it was always found, 
on referring to the laboratory notes, that a strong current, opposite in direction to that 
of the first one used, had been sent through the selenium, either a short time or some- 
times as much as a day, previous to these experiments. 
Polarization 'produced in the Selenium by the Current. 
The experiments described above, and others of a similar character, seemed to indi- 
cate that the electrical conductivity of selenium is electrolytic. It was therefore 
important to discover whether, after the passage of an electrical current through a piece 
of selenium, any distinct characteristic of polarization could be detected. The existence 
of polarization may be considered to be established if, after the current from a voltaic 
battery has been passed for some time through the selenium, and then the electrodes 
have been disengaged from the battery and connected with a galvanometer, a current 
in the opposite direction to that of the battery is found to pass through the galvano- 
meter. 
In the following experiments a modification of the ordinary commutator was employed, 
which has answered exceedingly well and is very simple. It consists of six boxwood 
mercury-cups screwed into a plate of ebonite at the angles of a 
regular hexagon, A, B, C, I), E, F. Into the cups A and D are 
dipped the electrodes of the selenium bar to be tested. F and E 
contain the battery-electrodes, B and C the galvanometer-wires. 
These cups can then be connected in any way feiat is desirable by 
means of short pieces of thick copper wire. Various pieces were made and amalga- 
B C 
• ® 
A • • D 
• • 
F E 
