210 PROFESSOR FORBES ON THE TEMPERATURE OF THE EARTH. 
On these results it may be remarked, that A, which is the logarithm of the 
superficial range, is necessarily variable according to the season, and that it ap- 
pears, singularly enough, to have been constantly on the decrease throughout the 
period of these experiments. This gives a great probability that the mean of 
these will be very nearly an average result for this climate. The depth at which 
the annual variation disappears is also evidently dependent, in part, on the qua- 
lity of the season. B is the only proper constant, depending solely upon the spe- 
cific heat and conductivity of the soil; and the mean results of Table X. are evi- 
dently near approximations to the truth. 
These computations have been made on the supposition that the logarithmic 
law of the diminution of the range is correct, and that the deviations from it are 
due to accidental errors. These deviations appear, however, to be too systematic 
to admit exactly of this conclusion. The observations at Craigleith coincide most 
nearly with theory ; those at the Observatory much less so, although there is every 
reason to believe that the observations there were in every respect the most un- 
exceptionable of the three. At the Observatory, the observations at great depths 
indicate a less rapid contraction of the range than do those at the surface, as an 
inspection of the curves in Plates IX. and X., and the points through which they 
have been drawn, sufficiently proves. 
To illustrate this difference, I had the constants A and B separately computed 
from all the possible combinations by pairs of the observations of 1837-38, with 
the following results. 


























D. Progress of Heat downwards. 
The curves of Plate VII. plainly shew that the periods of maximum and 
minimum temperature occur later and later as we descend. The epochs of maxi- 
ma and minima were obtained graphically at the same time with the greatest and 
least temperature, in the manner already described. The results are contained in 
the following Table :— 
a 




ah S 1-075 
TABLE XII. 
Observatory. Experimental Garden. Craigleith. 
2 12 Feet. 6 Feet. 3 Feet. 12 Feet. 6 Feet. 3 Feet. 12 Feet. 6 Feet. 
& A= 1:08 26 A Ha 26 ASS" 182 Ar 1180) | A 204 Ar Oi rac 1-077 Ace ere Ale . 
2 24 Feet. || p — —.0484| B = —-0510 | B = —0533 || B = —0465 | B = —-0475 | B = —0459 || B = —-0300 | B = —0294] B — —-0297}) 
ee en A= 1156 |A= 1-202 A= 1216 |A= 1-193 || A= 1-058 |A=— 1-069 
8 oo lhe Sus { B = — 0560 | B = —-0598 Seat She B= — 0495 | B = —-0476 oS Baas B = — 0283 | B = —-0293}) 
a pes PP eee Sees es = 
& |A= 1-225 A= 1-182 
s GUE 6 Sg 6 0 BG od oe {|B = 0674 } ee { i 2 geen } rec eee eee suc. > { B= —0318 
5 7 
Mean Values, . { as gee Mean Values, . { a ab Mean Values, . { a me 
j 
@ 
— 
