SUPPLEMENTARY REPORT ON METEOROLOGY. 83 
From which it appears that we have a progressive increase of 
temperature in the frozen soil, which, at a depth of about 400 
feet, will give a temperature just freezing. The augmentation 
would appear to be more rapid than usual, or 1° R. for 60 or 
70 English feet. ° ; 
126. Of observations in mines we have a most important and 
extensive series by Professor Reich, of Freiberg*, made under 
the most favourable circumstances, and with every assurance 
of their accuracy. They extend to a depth of above 900 feet, 
and the result of the combination of the whole is an increase of 
1° cent. for 41°84 metres, or 1° Fahr. for 76 English feet, with a 
probable error of only 1-37th partf. 
127. Professor Phillips found, in the Monkwearmouth coal- 
pit, an increase of 25° Fahr. for 1484 feet of descent, or 1° Fahr. 
for 59°36 English feett. The same gentleman has given valuable 
instructions for conducting such observations §. 
128. Mr. Fox gives 1° Fahr. for 48 or 50 feet as the results of 
his experiments in Cornwall||._ Mr. Henwood agrees with Mr. 
Fox in finding a difference in the progression of heat in slate 
(killas) and granite, and gives the following summary of his 
experiments J :— 
95 observations in slate 1°F,. for 39 feet. 
39 a, granite es 41°4 
This difference, Mr. Fox thinks, is probably attributable to 
the action of the mechanical structure of the rocks, in admit- 
ting superficial water**. 
* Beobachtungen iiber die Temperatur des Gesteins in verschiedenen Tiefen 
in den Gruben des Stichsischen Erzgebirges in den Jahren 1830 bis 1832, von 
F. Reich. 8vo. Freiberg, 1834. 
t+ P. 181. { Phil. Mag., Third Series, v. 451. 
§ Brit. Assoc., Sixth Rep., p. 291. || Ibid., Seventh Rep., p. 136, &c. 
§] Ibid., Seventh Rep., Sections, p- 36. 
** It will be seen that these experiments have no analogy in their objects 
with those made at Edinburgh on the influence of the material of the strata 
> tm the admission of solar beat, as Dove seems to suppose (Repertorium, 
. 307). 
A most important question, connected with earth-temperature, yet remains 
tobe decided. M. Kupffer maintains (see First Report, p. 224), that the super- 
ficial temperature of the earth exceeds that of the air in high latitudes, and 
falls short of it between the tropics (as was long ago asserted by Von Buch and 
others), and he has described Isogeothermal lines to express this fact. Bischoff 
maintains the contrary (Wdrmelehre, p- 38, &c.), declaring that Kupffer’s lines 
coincide with those of Humboldt (Isothermal), and that the warmth of springs 
in high latitudes arises solely from the depth at which they rise (p. 53), and he 
quotes the observations made by Boussingault, one foot below the surface (where 
he finds the temperature constant in tropical regions, and equal to the mean 
air-temperature of the year, dnn. de Chimie, liii, 225), in support of the 
assertion, that at the equator no difference of air- and earth-temperature exists, 
G 2 
