on the Electrical Resistance of Metals. 135 
of observations, and it was found that a scale division corres- 
ponded to a change in the resistance of about five-thousandths 
of one per cent. It will be noticed that the circuit was closed 
during the entire time of each set of observations. In view of 
ments by the damping method and found no diminution of 
resistance. The change, however, which he could have detected 
by this method was not much under one per cent. 
Ornstein’s second series of observations were entirely upon 
silver, deposited chemically on glass, and consisted of direct 
measurements of the ratio of the resistances of two plates by 
means of a Wheatstone’s bridge, with sliding contact wire. 
He exposed his plates to the light for periods of fifteen minutes 
each. The mean of his results shows a diminution of one and 
one-quarter hundredths of one per cent, which he attributes to 
the action of light. 
The experiments of Siemens and Hansemann seem to Born- 
stein to prove nothing concerning the influence in general of 
light upon the resistance of metals. For in them the plates 
were constantly traversed by a current, and moreover the 
illumination was. for exceedingly short intervals. As regards — 
the first condition, we know nothing of the influence of the 
electric current upon thin sheets of metal, and this influence 
should therefore be as much as possible done away with in 
searching for a delicate effect, and in the second place the light 
effect, if there is one, may take considerable time and the 
exposures should therefore be reasonably long. Bornstein 
therefore ascribes the fact that he obtains a different result 
from Siemens and Hansemann to his long exposures and to the 
fact that the current passed through his plates only during the 
short time occupied in making the measurements. 
The further discussion of these points is left until after the 
description of the experiments ree by the writer. : 
ese experiments were made in the Yale College Laboratory 
in a room from which light could be entirely excluded. The 
walls and furniture were painted black. The plates of metal 
used were five in number and will be distinguished by the 
