MACKIE— ON DE. FEANKXAND's GLACIAL THEOET. 163 
rises ; "the atmosphere," sajs Dr. Frankland, " is the true condenser, 
for the aqueous vapour that rises in it to its utmost heights radiates 
its heat into space ; the mountains are the receivers of the rain and 
snow precipitated." So far we have no objection to the doctrine. 
But to apply it practically to the production of the phenomena of 
the " Glacial period," which everybody knows was a geological period 
of intense cold, almost immediately preceding our own historical age, 
and possibly, according to recent ideas, absolutely including the early 
portion of the human era. Before this, according to the general 
tenor of geological notions, the earth had from the beginning of time 
possessed a gradually diminishing but still always higher temperature 
than it does at present; but whether this doctrine is not, upon 
stratigraphical evidences, open to grave doubts, we are by no means 
sure. Admitting this, for the sake of the argument, we have to see 
how Dr. Frankland applies Professor Tyndall's radiant-heat principles 
to the production of a period of intense cold. 
The points which he deemed his theory must meet are thus stated. 
The glacial phenomena must extend over the whole globe ; their oc- 
currence must be of geologically recent date ; they must have been 
preceded by ages during which glacial action was wanting ; and they 
must be followed by a time during which there was a re-tendency 
towards an ameliorated condition of temperature. Moreover, Dr. 
Frankland considers it essential to show that during their con- 
tinuance atmospheric precipitation was greater, and the snow-line 
lower, than at present. All these conditions. Dr. Frankland asserts, 
would naturally result from the gradual cooling of our planet ; so 
that, according to his view now put forth, " the sole cause of the phe- 
nomena of the Glacial epoch " — or period of universal intense cold 
all over the earth — " was a former higher temperature of the ocean 
than that which obtains at present." Admitting that our globe was 
once so hot that all the water now in it was then in nuhihus and not 
in the ocean cavities at all, he goes on to its first condensation into 
liquid, and then from the cessation of the boiling of the seas through 
a gradual diminution of temperature down to their actual state; a 
corresponding refrigeratidn of the land being contemporaneous. It 
was, he says, during the later stages of this cooling operation that 
the Glacial epoch occurred. For this result, however, he is con- 
strained to the assumption that the earth and the sea-water have 
cooled at different rates. To prove this he brought forward experi- 
ments upon the differences of cooling between a cube of granite and 
