DRIFT DIVISION. 
221 
mers are considered as having demonstrated that the length of our day has not varied a minute 
fraction of a second of time during the last two thousand years. Hence any sensible change 
in diameter, and consequently any increase of centrifugal force that should cause a flow of 
water from the polar regions towards the equator, with a more rapid current than that due to 
present causes, must have been antecedent to that time. This length of time having made no 
sensible difierence in the length of the solar day, might be urged as an objection to these 
views ; but mathematical investigations upon the laws of the refrigeration of heated bodies, and 
applications of those laws to the cooling of such a body as the earth, with the conducting and 
radiating powers of the materials forming those parts that have come under the observation of 
man, and with the temperature that it is known to possess, have shown that the time required 
to make any sensible difference in the mean temperature of its surface would be very great 
(almost infinite); and if such intervals are required for changes only sensible, what would 
they be for such changes of temperature as we have undeniable geological evidences of, in 
tropical plants and animals found in rocks of ancient date, even under the polar circles, and 
in the interior temperature of the earth, from observations in mines, artesian wells, and on 
hot springs and volcanoes ; and hence the time of two thousand years may be considered as 
the differential of such periods as geological phenomena and philosophical laws lead us to 
conclude have passed during the different geological epochs. 
Causes of polar currents. 
There are three supposable causes of currents flowing from the polar toward the equatorial 
regions, capable, it is believed, of producing all the effects and phenomena of the drift depo¬ 
sits, under the supposition that the land was mostly covered by water, viz : 
1. That arising from the refrigeration of the globe. 
2. That of the upheaving of large bodies of land or mountain ranges in the polar regions. 
3. That of the polar currents to restore the equilibrium, disturbed by the gulf stream and 
the difference of temperature of the water in the equatorial and polar regions. 
The first of these, arising from the effects of the refrigeration of the globe, has already 
been discussed, and found sufficient to produce currents from the polar regions towards the 
equator. 
On the second of these causes, namely, that of upheaved masses of land or mountains, at 
the period of the drift deposits, in the polar regions, we have no satisfactory evidence. Inves¬ 
tigations have not been made in those regions of the earth’s surface, sufliciently minute for 
drawing any conclusions; and the only evidence, that, as far as we know, would afford it 
any support, is, the effects observed farther towards the equator, in boulders and blocks 
transported in those directions, and scratches and abraded surfaces on the rocks in place, indi¬ 
cating a flow of water towards the equatorial regions. So long as there are causes sufficient 
to explain the effects, and on which there is strong and undoubted evidence, those possible 
causes on which we have no satisfactory evidence may well be discarded. 
