ne, 2 NOTICES OF THE MEETINGS [Feb. fl, 
nature are but branches of a common root, — what wonder, I say, if 
it jumped its bounds and cried ‘tI have it!’ too soon. For a 
long time the optic axis, and it alone, was chargeable with these 
phenomena, — phenomena which it was now hoped, there would be 
little difficulty in referring to their proper cause, and regarding as 
examples of the modification of force by the peculiarities of aggre- 
gation. 
The Lecturer then pointed out the bearing of the described results 
upon the problem of the diurnal range of the magnetic needle. Pro- 
fessor Faraday had referred the matter to the modification of atmos- 
pheric magnetism by the sun’s rays. That an effect was produced 
here could not for a moment be doubted, but the precise extent of 
this effect was still an open question. The discovery of a decimal 
period by Lamont threw a great difficulty in the way of any theory 
which would refer the diurnal range to thermic action; and the 
difficulty was greatly increased by the observation of Col. Sabine, 
who connected Lamont’s discovery with that of Schwabe regarding 
the solar spots. But whatever the result of future enquiries as to 
the direct magnetism of the sun may be, no theory which proposes 
to exhaust the subject can afford to omit the mediate operation of 
the sun by his heat ; not however confining it to the atmosphere, but 
extending it also to the earth’s solid crust. Let us look once more to 
our experiments. The line of greatest density is that of strongest 
magnetic power. The body operated upon by the magnet is itself a 
magnet, and it is an experimental fact, that it is a stronger magnet 
along the line of greater density than along any other line. If in- 
stead of increasing the density in one direction we increase it in all 
directions, we thereby augment the general magnetic power of the 
body. Anything therefore which tends to increase density increases 
magnetic power; and whatever diminishes density diminishesmagnetic 
power also. Knowing this, the conclusion is inevitable, that the 
local action of the sun upon the earth’s crust must influence, in some 
degree, the resultant effect. The action here meant is wholly diffe- 
rent from that hitherto speculated on, and which had reference to the 
generation of thermo-electric currents which affect the needle. The 
simple mechanical change of density is what is meant. It is a true 
cause, and no complete theory can omit taking it into account. 
The Lecturer then proceeded to remark on the influence of geo- 
logic changes upon the earth as a magnet, and concluded as follows : 
«This evening’s discourse is, in some measure, connected with 
this locality ; and thinking thus, I am led to enquire wherein the 
true value of a scientific discovery consists? Not in its immediate 
results alone, but in the prospect which it opens to intellectual 
activity, in the hopes which it excites, in the vigour which it 
awakens. The discovery which led to the results brought before 
you to-night was of this character. That magnet was the physical 
birth-place of these results; and if they possess any value they are 
to be regarded as the returning crumbs of that bread which in 1846 
a Y 
