70 Mr Hargreaves, Distribution of Solar Radiation, [Jan. 27, 



On L depends the total annual supply ; with no obliquity 

 its value is cos X, vanishing at the pole ; as the obliquity is in- 

 creased the value in low latitudes slowly diminishes, that in high 

 latitudes rapidly increases. The character of the resulting change 

 in distribution is first considered generally, and then with special 

 reference to the limits within which the obliquity is supposed to 

 vary, Stockwell's limits 21° 58' 36" and 24° 36' being used. Within 

 these limits the total range of L amounts at the equator to "93 

 per cent, of its present value, diminishes to zero in lat. 43° 20'; here 

 the sign of the change is reversed and the total range of L in- 

 creases up to 10^ per cent, at the pole. This alteration affects 

 both hemispheres alike. 



For the normal annual amplitude L x the total range is in every 

 latitude 10£ per cent, of its value, but this effect blends with 

 changes due to eccentricity, the influence of which appears on 

 transferring to mean time. This transformation is made for the 

 present position, numerical results being tabulated ; and also for 

 those positions in which eccentricity has its most pronounced 

 influence in modifying the annual term, viz. when the line of 

 equinoxes is at right angles to the major axis of the orbit, making 

 the inequality in duration of summer and winter greatest. 



If these epochs be described as genial and glacial, the first has 

 for element of heat-supply in north latitude expressed in mean 

 time 



2H 



-r- Q'dt, where Q' =L — (L x — 2eL ) cos 2irt. . . , 



while for the second Q"= L -f (L x + 2eL ) cos 2irt . . . ; 



only the more important terms of the coefficient of annual term 

 cos 2irt being here written. Attending only to these terms, in 

 high latitudes L x is large, and a high value of eccentricity is 

 required to produce any considerable modification. But L x 

 vanishes on the equator and is small in low latitudes, while L Q 

 has its greatest value there, so that a. moderate value of e makes 

 the difference between the two epochs quite considerable. One of 

 these formulae is derivable from the other by changing the sign of 

 L which is precisely the change made in passing from north to 

 south latitude. 



Hence in so far as change of eccentricity is a vera causa for 

 glacial epochs it acts in opposite senses in the two hemispheres, 

 making a genial epoch in the one contemporaneous with a glacial 

 epoch in the other. Also apart from the minute effect mentioned 

 at the outset, the action of eccentricity is through the periodic 

 terms, whereas the alterations due to obliquity affect also the 

 non-periodic term. The effects of changes in obliquity of the 



