1853.} OF THE ROYAL INSTITUTION. 955 
axes of calorific conduction ; the first and greatest axis being parallel 
to the fibre ; the second axis perpendicular to the fibre and to the 
ligneous layers ; while the third axis, which marks the direction in 
which the greatest resistance is offered to the passage of the heat, is 
perpendicular to the fibre and parallel to the layers. 
But it is the modification of the magnetic force by the peculiari- 
ties of aggregation, which forms the subject of the evening’s 
lecture. What has been stated regarding heat applies with equal 
force to magnetism. The observed magnetic phenomena are of a 
composite character. The action of a magnetic mass is the re- 
sultant action of its molecules, and will be influenced by the manner 
in which they are aggregated. The fundamental phenomena of mag- 
netism are too well known to render it necessary to dwell upon 
them for an instant. A small bar of iron was suspended in the 
magnetic field; it set its length parallel to the line joining the poles. 
Should we be justified from this experiment in concluding that a mag- 
netic mass will always set its longest dimension axial? No. A 
second magnetic bar, equal in size to the former, was suspended 
between the poles; it set its length at right angles to the line 
joining the poles. Whence this deportment? We find the reason 
of it in the mechanical structure of the bar: it is composed of mag- 
netic plates, transverse to its length: these plates set from pole to 
pole and hence the length of the bar equatorial. But let us proceed 
from this coarse experiment to one more delicate, where nature 
herself has imposed the conditions of aggregation. A plate taken 
from a mass of shale, picked up a few weeks ago in the coal district 
of Blackburn, was suspended between the poles; although strongly 
Magnetic it set its longest dimension at right angles to the line 
joining the poles. This deportment was at once explained by re- 
ference to the structure of the mass: it also, though apparently 
compact, was composed of layers transverse to its length; these 
layers set from pole to pole and hence the length equatorial. Let 
us ascend to a case still more refined. A crystal of sulphate of 
nickel was suspended between the poles, and on exciting the magnet 
a certain determinate position was taken up by the crystal. The 
substance was magnetic, still its shortest dimension set from pole to 
pole. The crystal was removed from the magnetic field and the edge 
of a penknife placed along the line which set axial ; a slight pressure 
split the crystal and disclosed two beautiful surfaces of cleavage. 
The crystal could in this way be cloven into an indefinite number of 
magnetic layers; these layers set from pole to pole and hence the 
longest dimension, which was perpendicular to the layers, equatorial. 
Comparing all these experiments,—ascending from the gross case 
where the laminz were plates of iron stuck together by wax, to 
that in which they were crystalline, the inference appears unavoidable 
that the unanimity of deportment exhibited is the product of a com- 
mon cause; and that the results are due to the peculiarities of material 
aggregation. 
