(2 rf. oe 
H. Hennessy on the Distribution of Isothermal Lines. 338 
heat received at any point of the earth’s surface from solar 
tadiation alone, abstracting the influence of atmospheric absorp- 
_ tion in different latitudes, varies in conformity wo Mayer's law 
_ asthe square of the cosine of the latitude. 
The more the influence of latitude predominates over all other 
causes, the more will the positions of the isothermals be changed 
in the manner above indicated: it follows, therefore, that while 
towards the equatorial coast of an island these lines terminate 
_ onthe coast, they may still continue as closed curves in the in- 
_ ‘norof the island. If the influence of differences of latitude 
| was greatly predominant over all other climatic influences, all 
the isothermals may terminate on the coast. 
| 5. The quantity of heat received by a given small area during 
the summer and winter half-years, between the spring and au- 
tumnal equinoxes, may be readily found by integrating with re- 
‘pect to u, within the limits 27 and ~, and afterwards within the 
'swand 0. Thus we shall have the general expression 
a2 Gm 
Sy { loos te) sin ha) +4, Ay] HH 
+ 2sinisin (4,+-4,)sin (4, —2,) t , (4) 
the term affected by 2 sind is to be taken with the positive si 
eu 
for that half of the year during which the sun is at the same 
for the other half of the year. —i, be so small that its 
May be neglected, then for the small area s=m(),—4,) 
We shall have the amount of solar heat H, received during 
year expressed by the equation 
4,= K(E(i)cos?A--sinisin2.4), making K= (5.) 
dene is always positive, as 4 cannot exceed 90°, it follows, 
“Telore, that the influence of latitude on poh ary of the iso- 
was Will be greater during the summer half of ‘th 
rein: the winter half ; and therefore, all other things remaining 
same, the isochimenal lines, or lines of equal winter tem- 
perature, would be less displaced from their concentric position 
*n island than the isotheral lines, or lines of equal summer 
side of the equator as the area in Spee and the negative sign - 
2 
2a72Gs 
the precedin expression we can determine the latitude 
din, zal ‘lich sactives the greatest amount of solar 
have the summer half of the year. For on differentiating we 
dH 
4g = KE (sinicos24—E(i)sin24), : 
eee 
of the yearthan - 
