W. L. Broun—Terrestrial Electrical Currents. 885 
Art. LVIII.—Experiment for Illustrating the Terrestrial Elec- 
trical Currents ; by Professor Wu. LERoy Brotn. 
THE following experiment enables a lecturer to exhibit to a 
large audience, in a very simple way, the action of the currents 
of electricity that pass around the earth. The experiment was 
suggested on reading an article by Professor om 
in the Philosophical Magazine for November, 1877. 
section three by two centimeters, whose sides were in length a 
fraction over a meter, and in breadth three-fourths of a meter. 
About the perimeter of this rectangular frame were wrapped 
twenty coils of insulated copper wire: each extremity of the 
wire was made to terminate near the center of one of the 
shorter sides, and passing through the wooden frame was 
fastened and cut off about three centimeters from the frame. 
This rectangular frame was then so suspended, in a horizontal 
position, by wires attached to the frame of an ordinary hydro- 
static balance, that the longer sides were at right angles with 
the beam. By adjusting weights in the pans the index of the 
balance was brought to the zero point. Two small orifices 
bored in a block of wood, a centimeter apart, served as 
When the current was reversed the deflection was in the oppo- 
site direction. By breaking and closing the circuit at proper 
intervals to augment the oscillations, the large frame was readily 
made to oscillate through an arc of five degrees. When the sides 
of the rectangle were placed northeast and southwest the current 
produced no sensible effect. A bichromate of potas 
of sixteen cells with plates of zinc and carbon, twenty-five by 
Six centimeters, was used. a 
With a rectangle containing a larger number of coils of 
Wire, attached to a very delicate balance, by using a consfant 
acting battery, the variation in the magnetism of the earth 
might thus be advantageously observed. 
