574 
PROFESSOR FORBES ON THE TEMPERATURES 
lities, and other causes, producing 1 inconsistencies so enormous that occasionally we 
are unable even to guess at them. Nothing is more common than to see the tempe- 
rature of springs set down at 212°, on the supposition that the escape of gas indicates 
actual ebullition. 
When we refer to any table of the temperatures of springs, the difficulty would be, 
not to point out which are erroneous, but which are correct. If this be the case even 
amongst the later observations, how much more must it apply to those of the last 
century ! M. Legrand of Toulouse has lately attempted to compare the tempe- 
ratures of the Eastern Pyrenean waters observed by Carrere in 1754 with the recent 
results given by M. Anglada. The former were probably made with the imperfect 
alcohol thermometer of Reaumur ; and though the latter were made by their indefa- 
tigable and estimable author, probably with all care and with good instruments, yet 
since (so far as I know) no examination of the scale of the instruments has been 
published, there may yet be errors of such magnitude as to diminish our confidence 
in future comparisons with them. Yet such results are amongst the very best we 
possess on this subject. It is remarkable, however, that in the memoir just alluded 
to, it has been shown, that if the observations were really made with the original 
instrument of Reaumur, in which the degree marked 80° was not the temperature of 
boiling water, but of the alcohol employed, the coincidence with Anglada’ s observa- 
tions becomes as close as could possibly be expected, and does not decidedly indicate 
any variation *. 
Temperature. 
Carrere, 
1754. 
Reduced to the 
modern scale of 
Reaumur. 
Anglada, 
1819. 
Nyer 
19- 0 
18-0 
o 
18-5 
Vinca (Source de Nossa) .... 
20-5 
19-4 
18-8 
Molitg (Grande Source) .... 
33-0 
30-3 
30-3 
La Preste (Grande Source) . . 
38-5 
35-2 
35*2 
Escaldas (Source du Milieu). . 
38*5 
35-2 
34-0 
V ernet (Source Exterieure) . . 
48-0 
43-0 
42-8 
Vernet (Source du Milieu) . . 
51-0 
45 5 
44-5 
Arles (Escaldadou Gros) .... 
55-5 
49-0 
49-0 
Thuez (Olette ; Carrere) . . 
70*5 
60-0 
60-0 
Enough has perhaps already been said to point out the importance of the inquiry, 
and the necessity of fixing data for future observers with a degree of accuracy hitherto 
unattempted. The application to the actual cases I have investigated will afford a 
better illustration than a mere detail of the required precautions would do ; whilst 
the remarks just made will explain the minuteness of local indication which I have 
entered into, and which might otherwise have appeared superfluous. 
With reference to the observations connected with the physical geography of hot 
* Comptes Rendus des Seances de l’Academie des Sciences, No. 7, 1835. 
