Review of Recent Geological Literature. 379 
ascertain the climatic conditions of any particular period was to pre- 
pare a map depicting with some approach to accuracy the former rel- 
ative position of land and sea. With such a map could our meteorol- 
ogists infer what the climatic conditions must have been? Yes, 
provided we could assure them that in other respects the physical 
conditions did not differ from the present. Now there is no period in 
the past liistory of our globe the geographical conditions of which are 
better known than the Pleistocene. And yet when we have indicated 
these upon a map, we find that they do not give the results which we 
might have expected. The climatic conditions which they seem to 
imply are not such as we know did actually obtain. It is obvious, 
therefore, that some additional and perhaps exceptional factor was at 
work to produce the recognized results. What was this disturljing 
element, and have we any evidence of its interference with the opera- 
tion of the normal agents of climatic change in earlier periods of the 
world's history? * * * * The success with which other problems 
have been attacked by geologists forbids us to doubt that ere long we 
shall have done much to dispel some of the mystery which still envel- 
ops the question of geological climates." 
Solar heat, Gravitation and Sun-xpots. J. H. Kedzie.' Two hun- 
dred and seventy-eight years ago dark spots were first discovered on 
the sun, and they have been the source of much discussion and re- 
search. Sometimes they are so large that they can be seen by the 
naked eye, covering millions and even billions of square miles. They 
frequent two belts on the pun's surface equi-distant from the equator, 
fading out along either edge. These belts of maximum freciuency 
extend from ten degrees either side to about thirty degrees north and 
south from the equator. They increase and diminish in fre(iuency 
at nearly regular periods of about eleven years. When they appear 
at the edge of the sun's disc their perspective clearly shows that they 
"are immense chasms in the strata of the photosphoric and penum- 
bral clouds, laying bare for the time the inner, darker and cooler 
nucleus of the sun." They are exceedingly variable in size and duration 
— the latter varying from a few hours to weeks or months. 
As already stated, the interest of the book culminates in the discu.s- 
sion of these spots, and in the application the author makes of his 
general theory to their explanation. A few more ascertaineil facts 
respecting the nature of the sun's photosphere an<l these spots will 
serve as an introduction to this explanation, viz : It has been deter- 
mined by actual experiment that the umbra emits fifty-four per cent, 
and the i)enumbra about eighty per cent, as much heat as a correspond- 
ing part of the photosphere. This shows that the heat of the pho- 
tosphere is not derived from the interior of the sun, and consoiiuently 
must come from without, from a supply independent of the internal 
heat of the sun. I'nd. Tlie lightest jjortions of the photosphere are the 
hottest. The faculai, "the sun's Himalayan mountains of light" are 
' For other portions of this review see pp. 181 , 246 and 300. 
