Electro-Magnetic Experiments. 379 
ed. M The neutralizing magnet. S The socket slitted and springy 
so as to move “ finger tight” on T. 
Experiments 1. Having adjusted the magnet to such height as near- 
ly to neutralize the effect of terrestrial magnetism, I brought the 
needle to north 45° west and raised a wine-glass of river water to 
the battery of the instrument, consisting of a five cent piece of silver 
and a corresponding disc of zinc. ‘The needle turned with an equa- 
ble velocity to the north, and finally quite to the east having descri- 
bed an arc of 135° in twenty one seconds. 
2. Having procured a rude piece of antimony and a strip of sheet 
copper I connected them with the wires of the galvanometer and fi- 
nally with each other, having previously warmed the copper by hold- 
ing it in my hands. ‘The needle was deflected 80°. 
3. I applied the two wires to the two extremes of the piece of 
antimony, which was about three inches long and one a half thick, 
pressing one wire to it with a piece of wood and the other with my 
thumb and finger. ‘The warmth of the hand, thus applied caused 
the needle to turn 76° when the wood and the fingers were changed 
to the opposite extremes, the needle reversed its motion. 
Whether the above experiments indicate any superior delicacy in 
the instrument I am not able to say. So far as my own experience 
goes, it excels by far all other modifications. 
I]. Experiments, March 12th, 1834. 
The most delicate experiments which I have made, are as fol- 
lows :— 
1. When the needle is nearly neutralized by the fixed magnet, 
the application of river water to the 5 cent piece battery will turn the 
needle 90° ; and often by impulse throw it entirely round. 
2. The poles (copper wires) of the instrument being held to the 
extremes of a piece of antimony as large as a hen’s egg, the one by 
a piece of wood and the other by the fingers, the needle will turn 
90° in consequence of the thermo-electricity generated by the heat 
of the fingers. ) 
3. Two discs of copper attached to the poles, and half an inch in 
diameter including a disc of antimony of the same size caused the 
needle to turn 90° upon the application of the end of the finger to 
one of the copper discs. 
Vor. XXVI.—No. 2. 49 
