OF WHICH VARIOUS SUBSTANCES ARE SUSCEPTIBLE. 
83 
general conclusions as to the precise ratio in which the energy increases with 
the separate quantities of matter, and decreases with the distance ; since both 
are involved in the experimental results. In the following Table is given the 
observed effect of each separate ring, as compared with the corresponding effect 
deduced by calculation from the first experiment, on the supposition that the 
energy is directly as the quantity of matter, and inversely as the squares of the 
respective distances ; and it will be seen that the differences are not greater 
than may, from the somewhat complicated nature of the experiment, be ex- 
pected. 
Table VIII. 
Rings 
No. 1. 
No. 2. 
No. 3. 
No. 4. 
No. 5. 
No. 6. 
No. 7. 
No. 8. 
Energy by cal- 1 
culation . . . . / 
4.5 
3.05 
2.19 
1.65 
1.28 
1.04 
0.84 
Observed energy 
8.54 
4.52 
3.45 
2.38 
1.83 
1.25 
1.25 
1.0 
25. There appears reason therefore to conclude, as a general principle, that 
the transient magnetic energy of any substance, not supposed to contain iron, 
varies in a direct ratio of the quantity of matter within the sphere of the action, 
and in an inverse ratio of the squares of the distances from the magnet ; the 
matter being supposed to be condensed into a stratum not having sensible 
thickness, and taken at some mean point of distance within the surface, 
where the sum of the forces may be imagined to produce the same effect as if 
exerted from every part of the mass; and the respective distances estimated 
between this mean distance and the opposed surface of the magnet*. 
26. It is a consequence almost necessarily resulting from the foregoing in- 
vestigation, that, supposing all other circumstances alike, the energy of the 
same substance is directly as its density, although such did not actually appear 
in the foregoing experiments with various species of wood (25) ; but this may 
be readily supposed to arise from the circumstance, that the energy of wood is 
* The reason why such should be the case for the magnet has been already given (12): it is 
equally applicable when the energy of the extremities only is supposed to be exerted : and it may 
be further observed, that although on either of the sides of a magnetic bar, the point of greatest at- 
traction of that particular side seems to fall (a little) within the extremity, yet the maximum of force 
of every common bar will be found invariably on the surface, terminating the extreme ends. 
