100 
MR. BARLOW ON THE PROBABLE ELECTRIC ORIGIN 
This is a highly important determination as it relates to the present inquiry; 
for here we have at once a demonstration that the earth is not a magnet, or at 
least that it does not act according to the laws of a permanent magnetic body, 
the distinguishing characteristic of which is, the existence of two poles, distinct 
and distant from each other ; whereas it is shown by this investigation, that in 
the earth these two poles are indefinitely near to each other and to the earth’s 
centre. 
M. Biot’s results, however, in consequence of the generality he had given to 
his first assumption, were involved in a very intricate formula ; but in the 
mean time a similar task had been undertaken by M. Kraft, of St. Petersburgh, 
on different principles. This philosopher contented himself with attempting to 
determine empyrically some mathematical formula to connect the different dip 
observations with each other ; and he discovered this very simple relation, viz. 
“ That the tangent of the dip of the needle in any place is equal to double the 
tangent of the magnetic latitude of that place.” M. Biot, in consequence of 
this deduction, re-examined his former investigation, and found that his for- 
mula after certain reductions, of which he was not before aware it was suscep- 
tible, became identical with that of M. Kraft ; and thus the fundamental law 
of terrestrial magnetism was confirmed by two philosophers acting apart and 
independently of each other, and on principles entirely different. It followed 
also from M. Biot’s formulae, that the intensity of the dipping needle ought to 
vary inversely as the square root of 4 minus 3 times the square of the sine of 
the dip ; and that of the horizontal needle inversely as the square root of 3 plus 
the square of the secant of the dip : conditions which have since been verified, 
at least approximatively, by observations, extending even to within one or two 
degrees of the pole itself. And these laws, I beg again to repeat, are entirely in- 
consistent with those which appertain to a permanent magnetic body, while 
they will be shown, in what follows, to be the fundamental laws of a body 
which receives its transient magnetism by induction. We see thus how it hap- 
pened, that those philosophers of the last century, who endeavoured to illus- 
trate the laws of terrestrial magnetism by what they called terrellse, or round 
natural magnets, with distinct poles, failed in all their attempts on this sub- 
ject to establish any mathematical principle of calculation. 
It has been seen that up to the year 1809, the phenomena of terrestrial mag- 
