266 On Sir G. C. Haughton’s Lxperimenis in Electricity. 
are put into play by the electrifying machine. ‘This may be 
easily shown by the following experiment. 
Take half an inch of copper wire, and suspend it, by a fila- 
ment of silk, in the centre of a vertical insulated metallic ring 
having an aperture of about an inch and a quarter. Electrify 
positively: both the ring and the copper wire, and the lat- 
ter will immediately place itself at right angles to the plane 
of the former. Now cause the needle to communicate with 
the ground for an instant; and, becoming of course negatively 
electrical by induction, it will be immediately attracted to the 
plane of the ring, and will vibrate from one side to another 
of it with the same energy as it did about the angle of 90°, 
when positively electrical. 
It is manifest, that the unstable equilibrium of the wire, 
when it is similarly electrical with the ring, and is also ex- 
actly in the same plane, may be converted into a stable equi- 
librium by superadding an attractive force which urges it to 
remain in that meridian. Hence it is that Sir G, C. Haugh- 
ton found that a delicately suspended magnetic needle re- 
mained steady, though a needle without directive energy was 
in similar circumstances deflected to 90°. 
The interesting and important case of static electrical ac- 
tion observed by Sir G. C. Haughton ought to be carefully 
guarded against by those who wish to ascertain the quantity 
of current frictional electricity by the multiplier. In France 
this instrument has been employed by M. Peltier for mea- 
suring the electricity of the atmosphere; and whilst it cannot 
be doubted that that able electrician used great precautions, 
the danger of the apparatus receiving a charge of electricity 
sufficient to interfere seriously with the results, cannot be too 
strongly urged upon the attention of those who repeat his ex- 
periments. 
I remain, Gentlemen, 
Yours respectfully, 
James P. JouLe. 
In my former paper, p. 205, the second sentence should 
read thus :— 
*‘ According to this the corrected theoretical result is, 10°*4’7 
minus one quarter of the heat evolved by the union of water 
and sulphuric acid, equals about 9°47.” 
Broom Hill, Pendlebury, 
near Manchester, March 4, 1843, 
