1896.] and its dependence on Ast?*onomical Elements. 71 



ecliptic are small in low latitudes, and well marked in high 

 latitudes ; those of eccentricity, with appropriate position of peri- 

 helion, are conspicuous in low latitudes, while producing a fair 

 modification in high latitudes. 



In each case the effects are so different in high and in low 

 latitudes that an average taken over so large a range as a hemi- 

 sphere quite obscures their special character. 



The question of drawing inferences as to temperature is 

 rendered extremely complex by a variety of modifying conditions, 

 of which the principal is the action of the ocean and atmosphere 

 as carriers and reservoirs of heat. Apart from these, a solution for 

 temperature may be easily obtained, but it is important to observe 

 that it is necessary to take non-periodic and the various periodic 

 terms separately, these being affected with different multipliers 

 in the integration, and the latter subject each to a different 

 modification of phase. This may render the comparison of terms 

 such as midsummer and midwinter heat with the corresponding 

 temperatures seriously fallacious. It appears to be important in 

 every case to compare non-periodic only with non-periodic under 

 other conditions, amplitude of annual term with amplitude of 

 annual, and so on. 



In order to estimate the effect of absorption, the transmitted 

 part is assumed to be equal to 



e + e x cos i" + e, z cos 2 / + . . . , 

 where / is angle between the rays and the normal to the surface. 

 This seems suited to express an absorption increasing as the 

 sun's altitude diminishes, with considerable generality, and has 

 the advantage that each term is exactly integrable in the manner 

 of the diathermanous case. 



This integration is effected, and some results tabulated, from 

 which it appears that in low latitudes the periodic terms are 

 exaggerated in comparison with non-periodic, the effect tailing 

 off as the pole is approached ; the amount of the absorption being 

 of course much less for low than for high latitudes. This relative 

 alteration ought to be taken into account in drawing conclusions 

 as to temperature. 



