Description of E. M. Clarke’s Electrepeter. 225 
the reversion of the electric currents, continuous rotary motion of 
the wire frame may be produced by the earth’s magnetism. ‘ 
_ A, A’, B, B’, four brass cups screwing into and passing through 
the bottom board. 4, b’, two brass pillars also screwing into and 
passing through the bottom board, having slits filed in their heads, 
into which two movable brass frames c, ¢’, fit, being connected by 
the two ivory rods d, d’; four brass studs a, a, a’, a’, screw into and 
pass through the bottom board, their upper surfaces being slightly 
concaved. The cups, studs, pillars and frames, are connected un- 
derneath the bottom board by pieces of copper wire soldered to 
them, as follows :— 
Cup A, and studs a, a. 
Cup A’, and studs a’, a’. 
Pillar 6, and cup B. 
Pillar 5, and cup B’. 
Consequently whichever pole of the voltaic, magnetic, or thermo- 
electric battery is in the cup A, the current passes on to the studs 
a, a, up the frame c, down the pillar b, on to the cup B. If you 
now reverse the position of the frames so as to bring their points in 
‘ connection with the other two studs, then the direction of the same 
eurrent will be from cup A, to stud a, up frame c’, down pillar 8’, 
on the cup B. It is only necessary to pour mercury into the four 
cups for the convenience of connecting the Electrepeter with the 
battery at one end, and the apparatus for the experiment at the 
other; it being immaterial which end you use. . 
lt may be necessary to mention that when I first constructed this 
instrument I showed it to Dr. Faraday, who thought he had seen 
one like it described in some of Arago’s papers; but on referring to 
his writings, he found that he had a contrivance for producing the 
same effect, but not so simple as mine. The Rev. T. W. M’Gauley 
- exhibited, in part of his very ingenious electro-magnetic experiments, 
an instrument to produce similar effects ; but on referring to p. 307, 
of the Philosophical Magazine for October, 1835, you will perceive 
mine is more universally applicable. 
‘Believing that no person is better qualified nor any one more de- 
serving of success in your present undertaking, 
I remain, sincerely, your obliged friend, 
. M. Crarxe, Magnetician. 
No. 9, Agar St. West Strand, London, Sept. 21, 1836. 
