SUPPLEMENTARY REPORT ON METEOROLOGY. 55 
C. Isothermal Lines*. 
45, We will despatch very quickly what is to be said on the 
very important subject of climatology, because no material 
step whatever has been made since the publication of the last 
report. A considerable number of detached observations, of 
various degrees of merit, on the mean annual and monthly 
temperatures of many points of the earth’s surface, have no 
doubt been added, and a list of many of these monographs may 
be found in Dove’s Repertorium+, and in the Transactions of 
the Meteorological Society. M. Kamtz has performed the use- 
ful labour of amassing all the trustworthy observations of mean 
temperature which he could discover, and presenting the monthly 
means, in the second volume of his Meteorology. The German 
translation by Mahlmann of my former report, embraces figures 
on different projections of the isothermal and isogeothermal 
lines. Both of these, especially the last, require still the greatest 
attention, even to give an approximation to truth; but we have 
not yet obtained the roughest sketch of the variations which 
these lines undergo with change of season; in other words, of 
the isocheimal and isotheral lines { ; yet these are of the greatest 
practical importance. The distribution of animal and vegetable 
life materially depends on them; the boundary of some plants 
being determined by the minimum winter temperature, and the 
advantageous cultivation of most by the extreme heat of sum- 
mer; the limits of the vine, maize, and olive depend on these 
circumstances ; and the region of barley so exactly coincides 
with the isotheral line, that (according to Wahlenberg) barley 
ripens wherever the mean temperature of ninety consecutive 
days rises to 48° Fahr. 
46. Professor Dove has not inaptly compared the annual 
variations of the form of the great system of isothermal lines to 
those which the Lemniscates formed in some biaxal crystals 
seen by polarized light undergo by changes of temperature§. 
47. These variations (to which we would particularly direct the 
efforts of meteorologists) are the more important, because, as 
we have already seen in treating of the form of the annual 
curve, places may have the same mean temperature, and yet 
their climates may have no real resemblance whatsoever (as 
when we compare the climates of Nova Zembla and Fort 
Franklin in North America, and those of Unst in Shetland and 
Copenhagen); and these characters may depend in a good 
measure upon local circumstances. Those who argue about 
* Last Report, p. 214, &c. Mahlmann, p. 45. } iil. 266. 
t Last Report, p. 218. § L’Institut, No. 325. 
