514 Intelligence and Miscellaneous Articles. 
The method we have used enables one to study the action of a celi 
at one’s own leisure, the apparatus running at night or during the 
day when one is occupied with other work. A beam of light from 
a gas-flame passes through a vertical slit placed in front of the 
flame, and is reflected from the concave mirror of a tangent-galva- 
nometer, of few turns of wire, through a horizontal slit, in a dark 
box, in which a sheet of sensitive paper is placed. By means of 
this arrangement of a vertical and a horizontal slit, 2 small point of 
light is obtained. A stationary concave mirror is placed near the 
needle of the tangent-galvanometer, so that the same beam of light 
may be reflected by both this mirror and the one attached to the 
galvanometer-needle. The spot of light given by the stationary 
mirror serves to mark the zero point of the needle when no current 
is passing through the galvanometer. The photographic paper is 
placed in a slide which is lowered uniformly by the unwinding of 
a string from a little cylinder placed either upon the hour-hand or 
the minute-hand of a cheap eight-day clock. When the electrical 
current from the voltaic combination, which is being used, passes 
through the galvanometer, its changes in strength for different 
times are indicated by the relations of the two lines drawn upon 
the sensitive paper. The line drawn by the light from the sta- 
tionary mirror is a straight one, and serves for the abscissa of 
times; while the perpendicular distances from the curve drawn by 
the mirror attached to the needle of the galvanometer to this axis of 
times give the ordinates of the curve drawn by the latter. Rapid 
printing-paper was used, and an ordinary gas-flame gaye a sufficiently 
strong spot of light to produce an actinic effect. 
Fig. 1 represents the action of a modification of Trouve’s battery. 
During this experiment, which lasted for thirty minutes, there 
were five ohms in the external circuit. The right-hand portion of 
en Fig. 2. 
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the diagram shows the strength of current when the circuit was 
made, and it will be observed that the battery was not at its best 
