AUEOKA BOEEALIS. 
137 
argument against the syllogism, condensed by himself into a 
a compact and telling form, was reduced to the logical form known 
as the dilemma. The reconciliation proposed by the lecturer, 
therefore, was, that logic should be defined as the science of the 
laws of thought, so as to comprehend both schools ; and that the 
science of logic should be subdivided into formal and material, the 
first investigating the formal laws, and the second the material 
laws of thought, and so severally relegated to the two schools, 
which henceforth should co-operate in friendly association for the 
common purposes of general science. 
AUEOEA BOEEALIS. 
ABSTRACT OF DE. HEARDEE's PAPEE. 
(Bead February 9tli, 1871.) 
The lecturer commenced by observing that the unusually brilliant 
display of the Aurora Borealis witnessed towards the close of the 
last year, particularly on the night of the 24th of October, had 
called forth remarks from different observers, scientific and un- 
scientific, which seemed to show that there still remains a con- 
siderable amount of obscurity of idea as to the real cause and 
definite character of the phenomena, notwithstanding the researches 
constantly being made in electrical science. 
The majority of observers seem to take it for granted that the 
phenomena which they witnessed were really the Aurora Borealis, 
whereas they were simply its refracted efi'ects, the Aurora proper 
which produced them having been far below the northern horizon. 
They were, in fact, to the Aurora proper what twilight was to the 
sun, and the exquisitely varied tints which seemed to envelope the 
canopy of heaven were produced by the same atmospheric condi- 
tions that gave rise to the gorgeous hues which heralded the ap- 
proach of the sun in the rosy morn, or which followed him after he 
had sunk below the western horizon with robes of golden light 
gradually fading into the soft and gentle twilight. 
The Aurora, as we observed it in our latitudes, assumed two 
appearances, which were occasionally observable at the same time, 
but were distinct in their character. The one was a widely-diffused, 
mellow, translucent tint of red or crimson, varying in depth of 
colour, and variegated by other prismatic colours, and the other 
