84 
MR. HARRIS ON THE TRANSIENT MAGNETIC STATE 
altogether too feeble to admit of such differences becoming appreciable by the 
means employed. In metallic bodies, however, the fact appears to be very de- 
cided ; thus, in three specimens of copper, whose dimensions were very nearly 
the same, but whose specific gravities varied, the resulting energies were ob- 
served to be the greatest in those which had the greatest specific gravity ; as 
for example, when the specific gravities were to each other as 8.30 to 8.40, the 
resulting number of vibrations amounted in the one instance to twelve, in the 
other to fifteen. To obtain more than rough approximations to the precise 
law by this method, would be extremely difficult, since the metals, as it is 
evident, should be procured in a state of great purity, and the dimensions, 
previously to taking the specific gravities, adjusted with an accuracy which 
only the most refined workmanship can effect ; there is however little doubt, 
if the experiment could be accurately tried, that the energy of the same 
metallic substance would, as a general result, be in the direct ratio of its 
density. 
27- It is of importance therefore, in estimating the comparative magnetic 
influence of metals, to take into account their density ; without which the 
inquiry might prove unsatisfactory. The energies of various metallic bodies, 
and some few alloys, were estimated by determining the number of vibrations 
of the bar between 45° and 10° in a ring of each; the metal being within 
0.1 of an inch of its poles. The more common metals were cast in a mould, 
and all the rings adjusted to the same dimensions. 
28. I endeavoured to estimate the energy of mercury at —50° of Fahrenheit, 
by freezing it into a solid ring, of the same dimensions as the preceding, in a 
mould of wood, accurately adjusted for the purpose ; but could only obtain 
satisfactorily, as a general result, the place it appeared to hold in the scale of 
magnetic energy. The ring was fully and completely solidified, and the mould 
so constructed as to admit of its interior part being removed, so that the needle 
could oscillate, whilst the metal remained externally enveloped in the freezing 
mixture. The thermometer, previously to removing the interior of the mould 
and adjacent salts, stood at —56°. I had not an opportunity of repeating 
this interesting experiment, which is sufficiently practicable, and seems to pro- 
mise the development of some new phenomena in magnetism. The energy 
of mercury in its fluid state, in a vacuum, was examined by inclosing it be- 
