THE 
LONDON, EDINBURGH, and DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOUKNAL OF SCIENCE. 
[FIFTH SERIES.] 
AUGUST 1883. 
XIII. Improved Construction of the Movable-coil Galvanometer 
for determining Current-strength and Electromotive Force in 
Absolute Measure. By Dr. Eugen Obach*. 
SOME years ago I showed that the tangent-galvanometer of 
ordinary dimensions may be employed as a measuring 
instrument for very strong currents if the ring is made 
movable around its horizontal diameter f , a principle already 
adopted before that time by Prof. Trowbridge, of Harvard 
College, Massachusetts % ; a little later I described a galvano- 
meter based upon that principle, and constructed by Messrs. 
Siemens Brothers § . 
I now propose to give a brief account of several alterations 
which have since been introduced by that firm, and which I 
venture to think render the instrument more sensitive and 
more convenient for use, besides creating for it a wider field. 
As the galvanometer, in the complete form in which I shall 
presently describe it, is not so much destined to meet the 
daily want of the practical electrician, but is rather intended for 
measurements where greater accuracy and trustworthiness than 
usual is necessary, I thought myself justified in bringing the 
subject before the Physical Society, particularly as the kindness 
* Communicated by the Physical Society ; read June 9, 1883. 
t 'Nature/ xviii. p. 707 (1878); Repertor. fur Exper. Physik. xiv. 
p. 507 (1878). 
% Amer. Journ. of Arts and Science, vol. ii. (August 1871). 
§ Zeitschrift fill- angewandte Electricitatslehre, i. p. 4 (1879). 
Phil. Mag. S. 5. Yol. 16. No. 98. August 1883. H 
