ABOUT TERRESTRIAL TEMPERATURE. 85 
the power as being in the meantime unknown. The expression for the temperature 
of the aqueous globe in a latitude \ may be thus expressed :— 
T,—=A+B cos” 2 
where A,B and m are constants to be found. Of course the equatoreal tempera- 
ture of the water globe will be A+B, and the polar temperature will be A. 
29. Fourthly, We will next, as an approximation merely, consider the effect of 
land in modifying the temperature of a given parallel to be proportional directly 
to the proportion of land on or near that parallel.* 
30. Fifthly, The general influence of land on climate is tolerably well known, 
and may be verified by the study of different climates. In every parallel of latitude 
the effect of masses of land or continents is to exaggerate the variation of tem- 
perature due to the seasons. The temperature of the ocean is more nearly uniform 
than that of continents. But besides this, as a general rule, the presence of 
continents affects the mean annual temperature, exaggerating the character of the 
climate, whether it be above or below the mean of the globe or hemisphere. It 
follows from this, that below a certain latitude the term in the expression for the 
mean temperature depending on the amount of land is additive; beyond that 
latitude it becomes subtractive; and in one particular parallel it is = 0, or the 
mean temperature is independent of the distribution of land and water. Thus 
the accumulation of land in intertropical Africa produces a temperature in excess 
of the mean of the parallel, while in Siberia the effect of the great concentration 
of land is precisely the reverse ; the temperature there is below the mean of the 
* If it were practicable to go into such details, it is probable that the influence of continents 
might be more accurately expressed by a different law from one depending on their simple breadth. 
A narrow land with ocean on both sides will have a slighter peculiarity of climate than if it were 
attached to a wide continent, and 
partook of a thoroughly continental 2 C 
character. In like manner, if ninety- 
nine hundredths of the circumference 
of the globe in any parallel were land, 
the small residue of ocean would 
affect the continental character of the 
climate even less than in proportion 
to its small extent. Let the circum- 
ference of the globe in any parallel ~~ 3 
be denoted by the le AB (=1); 
the fraction representing the land on the parallel by the abscissa AM (=L); let, also, BC express 
the extreme value of the term which expresses the effect of land on the temperature of the parallel ; 
then, for any value of L less than unity, the magnitude of the temperature-correction due to land 
would not be MN but Mn, which increases slowly when L is very small or very great, and most 
rapidly when L=}. Such a co-efficient might be adequately represented by such a function of L as 
a4 l—cos7L } 
2 

But such a mode of calculation would be perhaps a needless refinement, as we should have to take 
into account not only the sum of the land in the parallel, but also its continuity, or the contrary. 
VOL. XXII., PART I. ne 
