592 
PROFESSOR FORBES ON THE TEMPERATURES 
interesting, made their observations with Fahrenheit’s thermometer, which therefore 
are not liable to the error with which most observations of that period were charge- 
able, arising from the use of the imperfect dilute alcohol thermometer of Reaumur. 
We have, then, the following comparisons for Le Tambour : 
1739. Meighan 111|°Fahr. 
1750. Secondat* mentions five Douches, but they are all between 11 1° and 112° 
1826. Arago 44°-l cent. = 1 1 1°*4 Fahr. 
1835. My observations give 111°'9 
a coincidence very remarkable, and which there is no reason to believe accidental. 
I think it needless to refer to the observations which have been given of the other 
springs, as their temperature and relations seem to have materially changed. I am 
indebted to M. Balard of Bareges for almost the only definite statement I have been 
able to obtain as to the constancy of the temperature of hot springs at different 
seasons. He informs me (I translate from a memorandum made in his presence) 
that he has made perhaps ten series of observations on all the springs of Bareges 
between the months of June and September, and that he has not observed the tem- 
perature to vary by one tenth of a degree of Reaumur. This is a very interesting 
fact ; and it will be seen below that two experiments made by myself on the Douche 
of Le Tambour at the interval of a fortnight, and with very great care, do not differ 
by one tenth of a degree of Fahrenheit. 
Troughton. 
Reduced. 
1835, July 14. — Grand Douche, or Tambour 
. 112*0 
111-9 
Bain de l’Entree . . . 
. 104-6 
104-4 
Bain de la Chapelle . . 
88-8 
88 -7 
July 27. — Grand Douche .... 
. 112-0 
111-9 
Source Polard .... 
981 
97-9 
VI. Bagneres de Bigorre . 
A. Geological Position . — A superficial view of the environs of Bagneres would in- 
duce us to question the general application of the views we have given respecting the 
connexion of hot springs with intrusive rocks. But it is a very interesting fact, that, 
low as these springs occur, indeed at the very outskirts of the range, three distinct 
outbreaks of granite appear in the vicinity ; and though Bagneres itself is situated 
on limestone, clay slate is immediately connected with it. This granite has a re- 
markable structure. It consists in great proportion of felspar, is devoid of mica, and 
is extremely friable. It resembles much some of the decomposed granites of Western 
Cornwall. 
* Taken from Balard, Essai sur les Eaux Thermales de Bareges, p. 71. I have not now the work to refer 
to, otherwise I might ascertain whether the name of Le Grand Bain (synonymous with Le Tambour) occurs. 
