13A Geological Effects of a Varying Rotation of the Earth. x 5 
Fics. 7 and 8.—Germinating spores on May 5th, showing variations in mode of 
division, 
“ 9 and 10.—Young prothallia on May 8th. 
“ 11 and 12.—Young prothallia on May 8th, ene early branching. 
Fic, 13.—Short, thick prothallium (May 8th), 
“ 14.—Young prothallium, much elongated (May 8th). 
All the figures magnified 125 diameters. 
EXPLANATION OF PLATE II. 
ag 15. —Branching prothallium, May 18th 
16,— ‘giv: Map cue prothallium, showing protoplasm condensed in the ends of the 
cells 
“ 17,.—End of branch of older prothallium. 
“ 18.—Young antheridium. 
“ 19.—Antheridia; æ, unopened; 4, opened, with escaping antherozoid cells, 
June 13t 
Oi a + Prothalfias with antheridia and antherozoids, June roth. 
“ 21,—Antherozoids, mag. 
All the figures excepting Fig. 21 magnified 125 diameters. 
:0: 
ON THE GEOLOGICAL EFFECTS OF A VARYING 
ROTATION OF THE EARTH. 
BY PROFESSOR J. E. TODD. 
HE fact of variation in the velocity of the earth’s rotation, 
seems so nearly established as to call for a consideration of 
its effects on geology. One can scarcely read Professor New- 
comb’s masterly paper on the acceleration of the moon without 
feeling that the ability of astronomers to state the exact times of 
eclipses, especially of those in past time, has been, greatly over- 
rated. As he himself says in conclusion, “If Hansen is right, 
then Ptolemaic eclipses might be harmonized, but the Arabian 
would be ten to fifteen minutes out of the way, which to my 
mind seems very improbable. Apparently, therefore, we can 
hardly avoid accepting one of these propositions: Either the 
recently accepted value of the acceleration, and the usual inter- 
pretations of the ancient solar eclipses are to be radically altered, 
the eclipse of — 556 not having been total at Larissa, and that re) 
— 584 not having been total in Asia Minor ; or the mean motion of 
the moon is, in the course of centuries, subject to changes so 
wide that it is not possible to assign any definite value to the 
acceleration.” 
We learn from this same paper reasons for believing that the 
Newcomb. Observations on the moon before 1750, p. 278. (Washington Ast. 
and Met. Observations, Vol. xx, App. U.) 
