572 
PROFESSOR, FORBES ON THE TEMPERATURES 
under which the observations are made are liable to perpetual change. For instance, 
a spring in the state of nature may rise from rock directly, or from amongst debris. 
In the latter case, to fix the temperature is difficult, because it varies at different 
points ; and it is nearly useless, because a year hence the circumstances of its efflux 
may be wholly changed. Again, in the more usual case of thermal waters being 
medicinally employed, it is frequently impossible (at least without much trouble) to 
reach the true source of the water, which is carried through pipes, conduits, and 
reservoirs before it is finally employed ; and in this case the temperature is usually 
taken at the bath-cock, or at the c buvette,’ or drinking-cock, where consequently 
the water. has been subjected to the variable cooling action of its intermediate transit. 
Thus, for example, at the great establishment of La Railliere at Cauteretz, in the 
Hautes Pyrenees, the water is cooled from ] 0 1°*9 to 99 0, 8 in passing through a short 
and well-inclosed stone conduit from the source to the ‘ buvette’ ; and in the neigh- 
bouring spring of the Mahourat, the spout from which the water flows, though in 
contact with the granite rock from which it rises, and, in common parlance, the true 
or real source, I found to give a temperature 0 o, 5 lower than I obtained a few feet 
further back by squeezing myself into an almost inaccessible cleft of the rock. Thus 
for the most part we have no assurance that two travellers have observed the same 
spring at the same point ; and hence identity of name by no means infers compara- 
bility, even supposing the instruments perfect. The frequent alterations in the ther- 
mal establishments render a specific description of the locality still more indispen- 
sable. Where the mineral water is not applied to use, we have a new difficulty in the 
recognition of a spring by the mere description of locality. That hot springs should 
ever be so abundant as to render this possible might seem improbable ; I have had 
occasion to suffer from it, however, in following the footsteps of the indefatigable 
Anglada amongst the numerous and often almost inaccessible hot-springs of the 
Eastern Pyrenees (near Thuez, in Roussillon). 
There is almost a romantic interest associated with these vast bodies of hot water 
ceaselessly pouring from the heart of the earth, and for centuries together, as the 
Roman remains in the Pyrenees, in Auvergne, at Baden, at Naples, and in very many 
other places attest. But there is the far greater scientific interest attaching to the 
cause of phenomena so strange, especially where wholly detached from apparent vol- 
canic agency. Could we have known whether the temperatures of the waters have 
undergone any general change since remote times, the result would have been highly 
interesting and instructive ; yet we are not, even now , preparing for such future inves- 
tigations unless we commence a method of experiment commensurate with the accu- 
racy of the present state of science. 
The researches of Fourier lead us to believe that if the temperature of hot springs 
be due solely to that of the earth itself, at considerable depths, the changes during 
historic periods must be very minute. The chemical theory, first brought forward in 
relation to volcanos and since extensively adopted both in this country and on the 
