134 A. E. Bostwick—The Influence of Light 
series of experiments which are to be described in the present 
paper. 
Bornstein’s first series of experiments were made upon plati- 
num wires and thin leaves of gold, silver and platinum, mounte 
on glass. His principal methods were two in number. The 
first consisted in the comparison of the resistances of two wires 
or plates by means of a Wheatstone’s bridge, the plates being 
alternately illuminated. The second method consisted in the 
observation of the logarithmic decrement of the swing of a gal- 
vanometer needle, the galvanometer being coupled in a circuit 
with a single plate which was alternately lighted and darkened. 
The latter method is the one known as Weber’s method of 
damped vibrations. By these methods Bornstein obtained 
results, which, although alike qualitatively, differed a great deal 
‘in amount. Each set seemed to show that the resistance of the 
metals examined was diminished by light, but the diminution 
shown by the first method was only about one one-hundredt 
of one per cent, while that shown by the second was from three 
to four per cent. This difference Bérnstein accounts for by 
supposing that the passage of an electric current through a 
metal diminishes its sensibility to light. The metals would 
then be more sensitive when traversed only by the extremely 
feeble currents induced by the swinging needle, than when the 
comparatively powerful current necessary in the Wheatstone’s 
bridge was passing through them. Bornstein’s results seemed 
to show also that the action of light on the metals experimen- 
ted upon was greatest when they had been kept in darkness 
for some time, —a fact which had already been observed in the _ — 
case of selenium. 
_ The methods used by Siemens and Hansemann differed from 
both of those employed by Bérnstein. These observers made 
being thrown on and off the plates every twenty seconds. The 
movement of the needle during any period of illumination oF 
7 * its 
direction as often indicated an increase as a decrease of resistance. 
The sensitiveness of the galvanometer was tested at each series 
(ir 
pore tes 
Rie r i ios. = * 
RR ee: Mey ARTE ee ye eee Ny 
RoR ES eae | geen Se Fete : ie mee pee eh a6 
Saou & ciate ee pasate et Te, i Sen ites ‘ 
SRY Oe a oO Penn a, Sane an REL CET NPS cL er SN oman Tram er Eee Mae TOR RS ch Se) SR a en ee eG 
