436 Sir Graves C. Haughton in Reply to Mr. Joule. 
finger or any neutral body that was brought near them, while 
they stood at an angle of 90°, and even to give a smart, stinging 
shock, it was obvious that the insulation of the galvanometer 
had prevented the escape of the electricity, and though it was 
passing off at the other end of the wire that remained coiled 
up, yet still so considerable an accumulation had taken place, 
that every part of the galvanometer, including the needle, was 
highly charged; and that consequently by the law of similar 
states the needle placed itself at right angles to the frame of 
the galvanometer, being equally repelled by both its ends, and 
consequently took up that position, in which, to use mathe- 
matical language, there was an equilibrium of forces. This 
view suggested to me that the cause of the very small mag- 
netic needle (mentioned in my former letter) not being moved, 
was owing to its shortness, as much as to its polarity, and ac- 
cordingly I mounted a fine straw, one inch and a quarter in 
length on each of its points, and placed it in the galvanometer, 
when it was affected more sensibly than any other needle 
whatever, as might have been expected from its delicate con- 
struction. To put the matter however beyond all doubt, a 
sewing-needle was run through a slip of cork, upon which 
the needles were suspended in succession, and placed upon 
a plate of glass. One end of a piece of copper wire one foot 
and a half long and one eighth of an inch in diameter, was 
then placed on the cork and in contact with the sewing-needle, 
while the other end rested against the prime conductor, and 
immediately upon the machine being set in motion, any needle 
employed placed itself instantly at right angles to the copper 
wire. Whatever inclination was given to the wire, the needle 
under trial placed itself at right angles to it, which in fact was 
the only position it could assume, owing to the charged state of 
the wire and the needle. 
These experiments, as well as those of M. Becquerel, which 
Ihave already alluded to, show that the effects of heat and of 
repulsion ought carefully to be guarded against in the use of 
the galvanometer; and that whenever there is any degree of 
insulation, some repulsion may be anticipated, and which 
being added to the magnetic influence of the wire will give 
greater amplitude to the deflection of the needle, than would 
otherwise be the case. 
I am, Gentlemen, your obedient Servant, 
April 8, 1843, Graves C, Haveuton. 
