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POPULAE SCIENCE EEYIEW. 
that the air-breathers of the coal period are really the first species of their 
several families and then goes on to say , — “ Looking at them from this 
point of view, we shall first be struck by the fact, that they belong to all 
of the then great leading types of animals, which include our modern 
air-breathers — the Vertebrates, Articulates, and Mollusks. This at once 
excludes the supposition that they can all have been derived from each 
other, within the limits of the coal period.” * * * * * “ Again, 
our reptiles of the coal do not constitute a continuous series, nor is 
it possible that they can all, except at widely different times, have 
originated from the same source.” The peculiarity of Dr. Dawson’s 
reasoning is, that it commences with a petitio principii, and that apparently 
the Doctor is unaware that negative evidence of the kind produced neither 
supports his own doctrine nor militates against that of Mr. Darwin. 
The Earth’s Temperature in Baloeozoic Times . — Avery beautiful hypothesis 
has been framed by Mr. Sterry Hunt, F.R.S., to account for the increased 
temperature of the earth’s surface in former Geologic times. Adopting Pro- 
fessor Tyndall’s views on the subject of absorption of heat, he shows that 
during Palaeozoic times the presence of large quantities of carbonic acid 
in the atmosphere was sufficient to prevent the radiation from the earth of 
the heat derived from the sun, and thus to increase the temperature of our 
planet. Dr. Tyndall has shown that, heat from whatever source, passes 
through oxygen, hydrogen, and nitrogen gases, or through dry air with 
nearly the same facility as through a vacuum. Like rock-salt they allow 
of the transmission of heat ; glass, however, and certain other substances, 
although allowing heat to travel through them from luminous bodies, 
prevent its radiation from non-luminous ones. There are some gases 
which also possess this property ; thus the absorption of heat from a body 
at a temperature of 212 Fahr. is by vacuum 0, that by dry air 1, that by 
carbonic acid gas 90, that by marsh gas 403, that by olefiant gas 970, and 
that by ammonia 1195. So long as the earth is surrounded by a stratum 
of vapour, so long will radiation from it be retarded ; but during long nights 
the radiation into space causes the precipitation of a large quantity of this 
watery vapour, and so the protective shield is lost. However, we have 
every reason to believe that, during the earlier geological periods, all that 
carbonic acid which we now have in our various limestones, and as carbon 
in our coal formations, was distributed through the atmosphere. This 
having been the case, it is evident that the quantity of heat radiated from 
the earth during these epochs must have been vastly less than that 
which passes away in our times ; hence the temperature must also have 
been considerably higher, thus explaining why a vegetation like that of the 
tropics once existed within the frigid zones. In fact, the carbonic acid 
surrounded the earth like a huge protecting dome of glass. — Vide Canadian 
Naturalist and Geologist , August, 1863. 
Brachiopods new to the Lower Greensand of the Isle of Wight. — Mr. E. 
Ray Lankester records the presence of two Terebratuloe in the lower green- 
sand beds of the Isle of Wight, which have never before been found in 
these strata. He identifies them with T. Moutoniana of D’Orbigny, and 
T. depressa of Lamarck. “ The first is somewhat oval in shape, depressed 
and elongated ; surface entirely smooth.” The second has lenticular valves 
