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LV. On the Change of Eccentricity of the Earth's Orbit regarded 

 as a Cause of Change of Climate. By the Rev. Samuel 

 Haughton, F.R.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN the January Number of the Philosophical Magazine an in- 

 teresting paper is published by Mr. Jatnes Croll on the 

 Connexion of the " Glacial Epoch " with the Eccentricity of the 

 Earth's Orbit, founded on Leverrier's Memoire sur les variations 

 seculaires des elements des orhites pour les sept planetes princi- 

 pals, Mercure, Venus, la Terre, Mars, Jupiter, Saturne et Ura- 

 nus (Paris 1843), 8vo. 



In this memoir M. Leverrier calculates and gives a graphical 

 representation of the eccentricity of the earth's orbit for 100,000 

 years before the epoch January 1, 1800; from which it appears 

 that the unit of 10,000 years is sufficiently large to develope 

 the law of change, as the eccentricity in 100,000 years attains 

 two maxima and two minima ranging from 0*0473 to 0*0040, 

 or nearly in the proportion of 12 to 1. Under these circum- 

 stances it seems to me that Mr. CrolPs assumption of the unit 

 of 50,000 is not only unnecessary, but that it tends to mask the 

 real law of change of eccentricity. 



With regard to another and more imporlant point, Mr. CrolPs 

 paper appears open to objection. He fixes the times of greatest 

 cold at the times of maximum eccentricity, and infers the exist- 

 ence of two glacial epochs ; one 200,000 years before a.d. 1800, 

 when the eccentricity was 0*0569, and the other ranging from 

 950,000 to 750,000 years before the present epoch, with three 

 maxima of eccentricity, viz. 0*0517, 0*0747, and 0*0575. The 

 following are Mr. CrolPs words : — 



" We have already stated it as our opinion that the glacial epoch 

 of the geologist was the period beginning about 240,000 years 

 ago and extending down till about 80,000 years ago (' Reader/ 

 October 14, December 2 and 9). The time of the greatest cold 

 would be about 200,000 or 210,000 years ago. 



" It will be seen from an inspection of the Table that the next 

 glacial epoch prior to this occurred about 750,000 years ago. 

 At that time the eccentricity was exactly equal to what it was 

 210,000 years ago. Going back 50,000 years further, we find 

 the eccentricity to be only 0*0132. But 50,000 years still fur- 

 ther back, viz. 850,000 years ago, the eccentricity almost reached 

 its superior limit. It is quite possible that this, and not 200,000 

 years ago, may have been the period of the boulder-clay. Pro- 

 ceeding backwards the eccentricity is again found to diminish, 



