ARTICLE IX. 
On the Non-periodic Variations in the Distribution of Tempera- 
ture on the Surface of the Earth, between the years 1782 and 
1839. By Professor H. W. Dove, of Berlin*. 
THE mean temperature of the atmosphere is as little to be as- 
certained by immediate observation as the mean moisture or the 
mean pressure. It is concealed under manifold changes, of 
which we distinguish two kinds, periodic and non-periodic. By 
the non-periodic, those changes are meant whose regular or pe- 
riodic return cannot be ascertained with any certainty, and is not 
even probable. Meteorology has therefore three questions to solve; 
—first, the determination of the means ; secondly, the establish- 
ment of the laws of the periodic variations ; and thirdly, the as- 
signment of rules for the irregular or non-periodic variations : 
none of these problems have been as yet brought near a complete 
solution. 
_ The mean distribution of temperature on the surface of the 
earth was first and most naturally represented by Alexander von 
| Humboldt in his isothermal lines; the importance of this me- 
thod of representation, in regard to vegetation, has been shown 
| by Von Buch, Schouw, Wahlenberg, and Richardson. Brewster 
|and Kamtz have since employed more recent observations to pro- 
|duce a more accurate representation of the isothermals; Brew- 
\ster by the advantageous substitution of the equatorial for the 
polar projection, and Kamtz by drawing up special maps of single 
localities for which observations existed, and subsequently com- 
bining these in a general view. 
That the atmosphere does not exert an equal pressure on all 
| 
jticed the low barometer on the coasts of Norway, and the high 
‘barometer at the Canary Islands. 
| Humboldt had already shown that at the equator, where the 
air ascends, the pressure is diminished. Schouw has given a 
general view of what has been empirically deduced for the dif- 
erent zones. Daniell first attempted to show what part of the 
* Abstracted by Mr. Henry Croft, Teacher of Chemistry, London, 
