REPLY TO CRITICS. 39 



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 planetary 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 McFarlancl, with the aid of 

 Mr. Stockwell's formulae, has computed all the periods 

 in the tables referred to above.; and on comparing the 

 results found by both formulae, 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, and to 

 1,260,000 years after that date ; or, in other words, 

 over a period of no fewer than 4,520,000 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 increase in the quantity of snow 

 falling during that season. This very obvious result 

 follows as a necessary consequence from the fact that 

 the moisture which now falls in the form of rain would 



* In this laborious undertaking Professor McFarland computed, 

 by means of both formulae, the eccentricity of the earth's orbit and 

 the longitude of the perihelion for no fewer than 485 separate epochs. 

 See " American Journal of Science," vol. xx. p. 105 (18S0). 



