258 J. Croll—Geological Climatology. 
half, perhaps, is radiated back into space and lost, in so far as 
the earth is concerned. 
Tables of Eccentricity.—Referring to my tables of eccen- 
tricity of the earth’s orbit he says: ‘That there are from time 
to time such periods of great eccentricity is a well-established 
result of the mutual gravitation of the planets, but whether 
the particular epochs of great and small eccentricity computed 
by Mr. Croll are reliable, is a different question.” I may here 
mention that Professor McFarland, of the Ohio State Uni- 
versity, Columbus, a few years ago, undertook the task of 
re-computing every one of the 150 periods given in my tables, 
and he states that, except in one instance, he did not find an 
error to the amount of ‘001.* 
“The data for this computation,” continues Professor New- 
comb, “are the formule of Le Verrier, worked out about 
1845,+ without any correction either for the later corrections 
to the masses of the planets or for the terms of the third 
order, subsequently discussed by Le Verrier himself. The 
probable magnitude of these corrections is such that reliance 
cannot be placed upon the values of eccentricity computed 
without reference to them for epochs distant by merely a 
million of years.” 
In regard to this objection I may mention that the whole 
subject of the secular variations of the elements of the plan- 
etary orbits has been re-investigated by Mr. Stockwell, taking 
into account the disturbing influence of the planet Neptune, 
the existence of which was not known at the time Le Verrier’s 
investigations were made. Professor McFarland, with the aid 
of Mr, Stockwell’s formule, has computed all the periods in 
the tables referred to above, and on comparing the results 
found by both formule, he states that “the two curves exhibit 
a general conformity throughout their whole extent.” And 
his computations, I may state, extend from 3,260,000 years 
before 1850 to 1,260,000 years after that date ; or, in other 
words, over a period of no fewer than 4,520, years,} 
thus showing that Professor Newcomb’s objection falls to the 
ground, 
Influence of Winter in Aphelion—I have maintained that 
at a time when the eccentricity is high and the winter occurs 
in aphelion, the great increase in the sun’s distance and in the 
length of the winter would have the effect of causing a large 
* American Journal of Science, vol. xi, p. 456 (1876). 
Le Verrier’s formulz were worked out several years before 1845. 
. this rious undertaking Professor McFarland computed, by means of 
both formulz, the eccentricity of the earth’s orbit and the longitude of the perl 
helion for no fewer than 485 separate epochs. See American Journal of Science, 
vol. xx, p. 105 (1880), 
