74 Proceedings of the Asiatic Society. [ Marca 
The tester proceeds as follows :— 
After having cleaned the insulator carefully, he removes tem- 
porarily the line from the insulator and hooks the leading wire 
No. I to the iron hood and leading wire No. IT to the bracket of the 
insulator. He then turns the handle of the magneto-electric ma- 
chine with one hand, while one finger of the other is resting on 
the knob m of clamp e. 
As soon as he touches with the other finger the knob m/ of 
clamp c’, at the same time pressing it down, the metalic cir- 
cuit between ¢ and m’is opened, and the positive and negative 
magneto-electric currents have to pass from one finger to the 
other, and consequently, if strong enough, will give the tester sensi- 
ble shocks, by which he is at once informed that the insulator 
under test is defective, and much under the fixed standard of 
insulation. 
If the tester does not feel any current through his fingers, (a 
comparatively rough galvanoscop), he has only to repeat the ex- 
periment by placing his tongue on the knob m, while his hand 
still presses the knob m/down. If no current is felt by the tester 
through this most delicate galvanoscop, the tongue, he can rest 
assured that the insulator is perfect for all practical purposes. 
By opening and closing the circuit alternately at the knob m/, 
the tester has it in his power to allow at short interval currents to 
pass through his tongue, and consequently will be able to detect 
the slightest induction currents. 
The following experiments were made with insulators of known 
resistance to ascertain the highest limit by which the tongue is 
still able to detect induction currents. 
The currents in these experiments were produced by one of 
Siemen’s well known dial instruments, the revolving bobbin of 
which had a resistance = 1577 8. U. 
The absolute resistance of each insulator was first carefully 
measured in the ordinary manner, without water in the porcelain 
cups, and the insulator afterwards tested by the method above 
described, 
