due to the Eccentricity of the Earth's Orbit. 539 



tion lately opened up by him, I have asked Mr. Stone to allow 

 his calculations to be printed, without waiting till others of a 

 more complicated kind, and bearing on the same subject, are 

 completed. 



I have the honour to be, Gentlemen, 



Your obedient Servant, 



Charles Lyell. 



To Sir Charles Lyell, Bart., F.R.S., $c. 



Royal Observatory Greenwich, 



Sir, May 12, 18G5. 



The Astronomer Royal has placed in my hands your letters of 



1865, March 6, March 20, and May 8, together with Mr. Croli's 



papers, which I return : in part reply to your letters I have the 



honour to forward the following information. 



Assuming the sun's mean horizontal equatorial parallax 

 = 8" *943, and the Astronomer Royal's value of the equatorial 

 semidiameter of the earth = 3962 '822 miles, I find the mean 

 distance of the sun from the earth = 91,400,000 miles. From 

 Leverrier's paper in the Connaissance des Temps, 1843, 1 extract 

 the following values of the excentricity of the earth's orbit : — 



For the year 1800 

 Maximum value . 



=0-0168 

 = 0-0778 



From computation, I find for the values of the excentricity 

 210,065 years ago the value 



0-0575. 



These data give me the following results : — 



Years ago. 



Greatest dis- 

 tance of © 

 from © 



Least distance 

 of © from ©. 



Difference. 



65 

 210065 

 Maximum excentricity. 



92935521 

 90655504 

 98506355 



89864479 

 86144496 

 84293645 



3071042 

 10511008 

 14212710 



I consider that as the differences given above are nearly as 

 3:11: 14, whatever climatic changes may have taken place 

 through the existence of the absolute maximum excentricity, 

 corresponding and very slightly inferior changes must have taken 

 place about 210,065 years ago. As this period may therefore 

 turn out to be geologically interesting, I forward the values of 

 the excentricity and longitude of the perihelion of the earth's 

 orbit about this period. The longitudes are referred to the mean 



2N2 



