ABOUT TERRESTRIAL TEMPERATURE. 77 
which he did by the method which I have indicated above.* Preliminary to this, he 
had amassed and discussed an unprecedented amount of observations, as well for 
the mean annual temperature as for that of each month in the year.+ ‘The results 
form by far the most valuable body of information which we possess on this sub- 
ject. It is still, however, very much to be desired that M. Dove would add yet 
another to his various contributions to climatology; and that is a MercaTor’s 
chart on a large scale, and well engraved (similar to that of Dupsrrey for the di- 
rection of the magnetic needle), indicating all the places for which he has obtained 
the mean annual temperature, with that temperature (as reduced by him to the 
sea-level) engraved in figures on the chart, and the isothermal curves drawn 
amongst these figures, as M. Erman has so well done with reference to the mag- 
netic declination. At present we are deficient, not only of a precise and easily 
tested indication of the evidence on which the isothermal curves at any given 
part of the globe (and especially at sea) are determined, but owing to the small 
scale and rather rude execution of existing maps, and their occasional disagree- 
ment with one another, there is often a difficulty in making them as useful as they 
might otherwise be. M. Dove must be in possession of all the materials of such 
a chart; and it isto be hoped that he will add to the benefits which he has already 
conferred on the science of meteorology by its speedy publication. 
12. The “Thermic Anomaly,” of which I have spoken above, which is nothing | 
else than the expression of the effects of climatic influences not immediately de- 
pending on the latitude, is primarily due to the irregular distribution of land and 
water. Were the earth’s surface homogeneously constituted, were it all land or 
all water, the symmetry of the different meridians would be perfect,—there could 
be no assignable cause for a variation in the gradation of climate from the equa- 
tor to the pole depending on the longitude. The isothermal lines would coincide 
with the parallels of latitude, and the inflections of the isothermal lines, which, 
in the language of M. De Humsoupt, are precisely what the thermic anomaly is 
in the language of M. Dove, would cease to exist. 
13. The irregular intermixture of oceans and continents acts primarily by the 
inequality of the absorption and detention of the solar rays by land and water, and 
by the laws of conduction and of convection which regulate the internal motion of 
heat in the one and in the other. But, secondarily, the consequences of this irregu- 
larity are not less important in producing currents of the air and ocean. Heat 
* The Distribution of the Heat of the Globe, &c., p. 18, &c. London, 1858. [The same work 
was published in German at Berlin. In point of fact, the annual mean temperatures of the parallels 
are derived by M. Dove from the average of the twelve months separately considered, and projected 
in monthly isothermal lines. It would probably be preferable to deduce them from the annual curves 
alone, which rest on a surer basis. ] 
+ See his “ Five Memoirs” in the Berlin Transactions, “ Ueber die nicht periodischen Aenderun- 
gen der Temperatur vertheilung aufder Oberflache der Erde,” and his “Temperature Tables,” in Re- 
port Brit. Assoc,, 1847, 
