16 
than all the known period of human history, aboriginal men, 
who possessed no arts, and left no monuments, and lived in 
the dark with no message of light from heaven, must have 
continued to wander, homeless and hopeless, in deserts and 
mountains, and in dens and caves of the earth. 
The moral and religious difficulties of such a creed are plainly 
immense. I wish now to examine it simply on the side of 
physical science. Mr. Croll’s theory is certainly elaborated with 
great pains and care, and includes a wide collection of materials, 
and a large amount of patient thought and ingenuity. It has 
received the highest praise from a writer in the Quarterly 
Review , as beautiful, simple, and complete. I need, there- 
fore, to offer strong reasons for my own conviction, expressed 
before in the Annual Address, that it is based on a complete 
fallacy, and is wholly wanting in solidity and truth. 
27. A first objection, made by Professor C. Martens, and 
more recently by Mr. Callard, is of a very simple and striking 
kind. The planet Mars is forty millions of miles further from 
the sun than our earth. Its excentricity is - 0933 instead of 
*01678, or 5^ times greater, and its absolute amount 26 millions 
of miles, or nine times greater than the present excentricity of 
the earth ; three times greater than that at Mr. Croll’s second, 
and twice as great as at his first, supposed glacial period. Yet 
the snows of this planet, while they increase in winter, and 
decrease in summer, are never seen to extend more than six or 
seven degrees from either pole. The spectroscope and tele- 
scope conspire to prove that Mars is not now suffering under 
an ice age. How, then, could the increase of the earth’s 
excentricity from 3 to 10^ millions of miles produce the 
glaciation of more than half the hemisphere, when one of 
26 millions has no such effect in a planet half as far again 
from the sun ? 
Mr. Croll observes that little is known of the climatic con- 
dition of Mars, and that its atmosphere may perhaps be wholly 
different from our own, and that other physical conditions, 
besides greater excentricity, may be needed to secure a glacial 
epoch. This may doubtless be true; but since we have only 
to guess at such causes of difference, the negative evidence, 
though not decisive, is strongly adverse to the notion that 
glaciation, in the case of our earth, is duo mainly to a greater 
excentricity than now exists. For in Mars the aphelion dis- 
tance is about 148 millions, while in Mr. Croll’s ice era, our 
own would be 97 millions, and still the imaginary result from 
increased excentricity does not seem to follow. 
28. A second objection has some weight. The total heat 
received by the earth in a year from the sun is inversely as 
