M. Hiiraboldt on^ Isotliermal Lines^ and the 
When we consider that the annual temperature of a place is 
nothing more than the numerical expression of the mean of the 
ordinates, we may imagine an infinity of entirely dissimilar 
curves, in which the twelve ordinates of the months have exact- 
iy tlie same mean. This consideration should not lead us to 
believe, that a place which has the winter of the south of 
France, that is, where the mean temperature of winter is 44^.6, 
may, by the compensation of a summer and an autumn, much 
less v/arm, have the mean temperature of Paris. It is true, that 
the constant ratio which is observed in the same parallel, be- 
tween the solstitial heights of the sun and the semidiurnal arcs, 
is differently modified by the position of a place in the centre of 
a continent or upon the coast, by the frequency of certain 
winds, and by the constitution of an atmosphere more or less 
favourable to the transmission of light, and of the radiating ca- 
loric of the earth. But these variations, which travellers have 
often exaggerated, have a maximum which nature never over- 
steps. It is impossible to examine the preceding table without 
observing, that the division of the annual heat between summer 
and winter, follows on each isothermal line a determinate type ; 
that the deviations of that type are contained between certain li- 
mits, and that they obey the same law in the zones which pass 
by the concave or convex summits of the isothermal lines, for 
example, i)y 58°— -68° of West Long,, and by 5°— 7% and 116° 
of East Longitude. 
The following table shews the oscillations, or the maxima and 
mmima, observed in the division of the heat between the sea- 
sonsi I have added the means of the winters and summers 
found at different degrees of longitude, and under the same iso- 
thermal line. 
isoth. 
Lines. 
Degrees of 
Long, exa- 
mined. 
Oscillations observed 
Means. 
in the 
Means calculated. 
W inters. 
Summers. 
W inters. 
Summers. 
33® 
83 
3“.2to24°.8 
51°.8 to 53°. 6 
14°.0 
52°. 7 
41 
iOT 
14.0 
24.8 
62.6 
68.0 
19.4 
65.3 
50 
300 
23.0 
37.4 
62.6 
78.8 
30.2 
70.7 
59 
87 
39.0 
44.6 
75.2 
77.0 
41.9 
75.2 
j «8 
84 
53.6 
59.0 
71.6 
80,6 
56.3 
77.9 
