THE PLANETS. 459 



very different periods of the year, in consequence of the 

 alteration in the position of the major axis.* 8 If the perihelion 

 falls at the present time on the first day of January, and the 

 aphelion six months afterwards, upon the first day of July, it 

 may happen on account of the advance (turning) of the 

 major axis of the Earth's orbit, that the minimum may occur 

 in summer and the maximum in winter, so that in January 

 the Earth would be farther from the Sun than in the sum- 

 mer, by about 2,800,000 geographical miles (i. e. about ^th 

 of the mean distance of the Earth from the Sun). It might 

 at the first glance be supposed that the occurrence of the 

 perihelion at an opposite time of the year (instead of the 

 winter, as is now the case, in summer), must necessarily 

 produce great climatic variations ; but, on the above suppo- 

 sition, the Sun will no longer remain seven days longer in 

 the northern hemisphere; no longer, as is now the case, 

 traverse that part of the ecliptic from the autumnal equinox 

 to the vernal equinox, in a space of time which is one week 

 shorter than that in which it traverses the other half of its 

 orbit from the vernal to the autumnal equinox. The differ- 

 ence of temperature which is considered as the consequence 

 to be apprehended from the turning of the major axis (and 

 we refer here merely to the astronomical climates, excluding 

 all considerations as to the relations of the solid and liquid 

 portion of the many-formed surface of the Earth), will, on the 

 whole, disappear,* principally from the circumstance that the 

 point of our planet's orbit in which it is nearest to the Sun is 

 at the same time always that over which it passes with the 



48 John Herschel on the Astronomical Causes which may 

 influence Geological Phenomena, in the Transact, oj the Gcolog, 

 Soc. of London, 2nd series, vol. iii. pi. i. p. 298 ; the same 

 in his Treatise on Astronomy, 1833. (Cab. Cyclop, vol. xliii, 

 315.) 



44 Arago, in the Annuaire for 1834, p. 199. 



