215 
Causes of Cosmical Changes of Temperature on our Planet. 
It is admitted that the possible changes in the present meteorological 
conditions of our planet could not account for the great fluctuations of tem- 
perature recorded in the geological history of the glacial periods. Mr. 
!S. J. Mackie, in the last number of the 'Geologist,' attributes these 
changes of temperature to changes of size of the sun's disk, to maximum 
and minimum periods of solar heat, etc. etc. It is clear these explanations, 
although possible, are purely arbitrary, mere speculations, unsupported by 
any cosmical or physical facts. Xow, it is known that our solar system is 
travelling in space towards the constellation Hercules at tlie rate of 57| 
miles a second ; yet so great are star-distances, that thousands of years 
elapse before our risible position in the heavens be changed to the naked 
eye. From the observations of Glaisher in his balloon ascents, it appears 
tluit the decrease in temperature is not in direct proportion to the distance 
from the earth ; but, on the contrary, tliat a liundred feet elevation at the 
earth's surface produces as great refrigeration as a thousand feet at a 
greater elevation. It necessarily follows that we must arrive at cosmical 
temperature bcA'ond the influence of atmospheric changes ; but is this 
cosmic temperature uniform through the portions of sj)ace destined to be 
traversed by our solar system ? If there be portions of space of different 
cosmical temperatures through which our planet has passed, this would 
account for the great cold of the glacial periods in a way supported by one 
strong fact, ^A■hich is, that our position in the heavens is changing at the 
rate of o7\ miles a second, and for this change of position not to affect the 
heat of our earth, we must suppose the cosmical temperature of space so 
traversed by our earth to be uniform, which would be a most arbitrary 
supposition. It is quite possible, nay even probable, that not only our 
own solar system, but all visible creation, the infinite and countless stars, — 
so remote, that their light has taken millions of years to come to our eye, — 
are all revolving through space around some almost infinitely far-off" centre, 
■which if luminous, its light is so attenuated by distance as to be invisible 
to us. and that the period of such a revolution may be long, beyond all 
calculation, during which immense portions of space must be traversed, 
most likel}' of unequal cosmic temperature, quite sufficient to account for 
the glacial periods in the geological history of our earth. There is nothing 
fanciful in this view, or beyond the range of probability. The vast luagni- 
tude of such a system is no objection to its existence, for, in comparison 
■with infinity, all assignable distance or magnitude shrinks into a mere 
point. The immense period necessary for such a revolution ■would afford 
ample time for all the glacial formations recorded by geological observa- 
tion, by admitting only the natural supposition that the temperature of 
infinite space is not uniform. Yours, etc., David Leslie, M.D. 
Carrickmacross, Ireland, M.ay 21, 1863. 
[It is not the intention of the Editor to reply to comments on his articles in all cases 
separately, but in one or two respects Dr. Leslie's letter reqnircs notice. Mr. Mackic 
distinctly put forward the views in his paper as speculations ; but Dr. Leslie is wrong 
in saying they are all unsupported by physical or cosmical facts. Neither is it admitted 
that possible changes of meteorological conditions could not have produced the cold of 
the glacial era. It may have been dogmatically asserted so. "We should be glad to 
learn what temperature Dr. Leslie thinks existed then, and what were the tluctuations it 
was subjected to. We should also be glad to know on what grounds the idea of hot 
and cold regions in space can be maintained ; and why the cosmical temperature of space 
should not be the real zero of temperature, or a condition of absence of all heat. We 
should like to know what is the presumed temperature of the cold cosmical space through 
■which our globe is so hypothetically supposed to have passed in the glacial age.— Ed. 
Geol.] 
