SECTION III., 1900 ae Trans. R. 8. C- 
X.—A Universal Electrical Measuring Apparatus. 
By W. Lash MILLER, B.A., Ph.D. 
AND 
F, B. Kenricx,—B.A., Ph.D. 
(Read May 30, 1900.) 
Measurements of volts, ampéres, ohms and mhos, their multiples and 
sub-multiples, can all be reduced to galvanometer zero methods, involv- 
ing the variation of one resistance only. The writers have taken advan- 
tage of this fact to construct an instrument which alters the resistance 
in question automatically, and which can, in consequence, be used for 
measuring electromotive force, current, resistance or conductivity as de- 
sired. The apparatus, as constructed in the Chemical Laboratory of the 
University of Toronto, is aperiodic, and is provided with a large dial 
(two feet in diameter), two details which render it of service in the lecture 
room as well as in research work. 
The essential parts of the instrument are (A) a galvanometer, (B) 
two relay circuits, one of which is closed when the galvanometer needle 
swings to the right, the other when it swings to the left of the zero posi- 
tion, (C') a mechanical device (controlled by B) for increasing and de- 
creasing the variable resistance, (D) a series of subsidiary resistance 
coils and a means of quickly making the necessary connections, and (Æ) 
a commutator. 
THE GALVANOMETER AND RELAYS. 
The galvanometer is constructed on the d’Arsonval model, but, as 
constancy of the magnetic field is not essential, the usual steel magnets. 
are replaced by a powerful electromagnet. This increases the delicacy of 
the instrument and ensures good damping. 
In figures I. and IL., Wis the electromagnet, G the coil of the gal- 
vanometer, to which is rigidly attached the glass fork f moving the lever 
h pivoted at n,n. Contact made between h and a (or b) completes the 
circuit of a relay which closes the contact r (or 1). See fig. III. 
THe MEcHANICAL COMPENSATOR. 
The duty of this part of the apparatus is to increase or decrease an 
electrical resistance, according as the galvanometer relay makes contact 
ataorb. The variable resistance consists of 203-7 ohms of special resist- 
ance wire zig-zagged on the surface of a wooden wheel W (figs. IV. and 
