dove’s TEMl’ERATL'UE TABLES. 
375 
Africa, New Holland, New ZeaUviul, or the Falkland Islands, witli stations 
in corresponding latitudes in the northern hemisphere, wc find a similar 
result, though varying, as might be expected, in the amount of difference at 
the two periods of the year; but all testifying that the aggregate mean tem¬ 
perature at the surface of the globe is greater in June, July and August, 
than in December, Junuary and rebmarv. This is a result of tlu* uneijual 
distribution of land and sea in the two hemispheres, and of the <lifference 
in the effect produced by the sun’s heat according as it impinges on a solid 
or on a liquid surface. It is well-known that llritain is nearly the middle 
point of an hemiaplien? distiuguiehed by the preponderance of land at the 
surface, and New Zealand the middle, or nearly Bt», of au hemisphere di¬ 
stinguished by the preponderance of an aqueous surface. The greater pro¬ 
portion of land is consequently in the northern lietnisphere as taken with 
reference to the sun’s path ; whilst the southern hemisphere has the greater 
proportion of ocean surface- The existence of a periodical variation of the 
aggregate, mean temperature derived from the sun, might thence have been 
(and possibly may have been) anticipated, but it i$ now made know n to us as 
an experimental fact, by the iuu<iern practice of systematic observation, and 
of the intercomparison of mean numerical results so obtained. 
2. Tlie differences between the hottest and the coldest months of the 
year, w'hich form a part of the results of Professor Dove's iDvestigation, are 
a very important clement in Judging of clinmtlc relations. 
If the iutcreompariBon of these differences bo extended so as to include 
places W'hich differ in latitude as well as in other circumstances by which 
climate is infliienccd, we may find in these tables striking examples of the 
great diversity which takes place in different parts of the globe in the dis¬ 
tribution of the niciui temperature of the year into its several mouths and 
^easions. Thus if we refer to C'ommcwiiic lu Guiana, and Jakutsk in Siberia, 
w'c find the difference between the hottest and coldest months to be ^°*2 of 
Fahrenheit at Connnewinc, and U4'H at .labutsk ; ami if we limit the 
comparison to places wliich correspond in latitude, to stations for example 
in Northern A.sia compared with others In liunipe or in North America, we 
^hall still find that the diversity is very great in this respect 
The terms of lusular ami Continental climates have been employed to 
clinracterise respectively those climates in which the difference of the mean 
temperatures of the hottest and coldest months is very small, and those in 
which it is extremely largo. 
The distinction thus eslahlislied and the designations so employed have 
been understood to refer exclusively to the ilifferenccs between the extreme 
t<'mperatun.*8 either of months nr of seasons, and to he irrespective of the 
absolute meun temperature of the year, season or montli. It is obvious how- 
fver that circumstniiees might exist, which would cause the mean temperature 
of the coldest month, for example, at a station to be extremely low when 
viewed in reference to what might be regarded as the normal temperature of 
that month eorresfionding to the parallel of latitude, whilst other circum¬ 
stances might be wanting which would occasion the mcatr temperature of the 
hottest month to be excessive in the other extreme, when compared in like 
manner xvilli a normal temperature correspondiug to tlie latitude; or vice 
rersdi that tlje temperature of the hottest tnonlh might be excessive in re- 
sjKfCt to Ijeat, whilst that of the coldest month might not suffer a correspond¬ 
ing depression. In such eases the mere difference between the temperatures 
of opposite seasons or of the extreme mouths, irrt^iJcctive of the difference 
of the temperature of either from a normal temperature, would fail to render 
muiiifest and to distinguish tlie peculiarity which prevniU during one portiou 
