SUPPLEMENTARY REPORT ON METEOROLOGY. 85 
difference of observed temperatures is not, however, the same, 
because the one spring rose from a greater depth than the 
other. The variation due to this cause then becomes apparent ; 
and the difference of depth from which they rise being known, 
the rate of increase is found by M. Kupffer to be 1° Fahr. for 41 
English feet ; a process which must be admitted, at all events, 
to be extremely ingenious. He has treated some of Wahlen- 
berg’s observations in a similar way*. 
131. On the subject of hot-springs, or those which have a 
temperature notably higher than that of the air, (though, as 
Bischoff has well remarked, there is an insensible gradation,) 
we cannot now enter; and this is the less to be regretted, as 
Dr. Daubeny has already presented an ample report to the 
British Association on the subjectt. M. Arago has published 
some valuable remarks on the same subject, especially on the 
curious phenomena of the springs of Aix in Provence{. With 
a view to direct the attention of naturalists to the secular and 
annual changes of temperature in hot-springs, I have made 
some very detailed investigations on this subject, which I have 
published, as far as relates to those in the Pyrenees§. The 
central heat theory would require these to be insensible, as 
indeed they appear to be in the best known instances. 
IIl.—AtTmosPHERic PREssuRE. 
A. Barometers||. 
132. The standard barometer of the Royal Society of London 
has two tubes, one of flint, the other of crown glass, adapted to 
a common cistern, with a view, it is believed, of ascertaining 
whether any change in the capillary action occurs, depending 
on the nature of the tube. The scale, according to Dr. Prout’s 
ingenious construction, is itself moveable, its zero coinciding 
with a fine agate point, which terminates it, and which may be 
brought into the nicest contact with the mercurial surface in 
* In Prof. Kimtz’s Lehrbuch der Meteorologie, ii. 186, &c., is much valu- 
able information on the subject of springs; also in Dove’s Repertorium, 
ili. 310, 
¢ British Association, Sixth Report, pp. 1—95. 
{ Annuaire du Bureau des Longitudes, 1836, p. 265 ; see also M. Valz’s com- 
munication, Comptes Rendus, vol. x. 
§ Phil. Trans. 1836. On the subject of hot springs, Osaun’s work in 2 vols. 
8vo. (Europa’s Heilquellen, Berlin, 1829), may be consulted in German, Ali- 
bert’s in French, and Gairdner’s in English ; but the temperature observations 
seldom afford more than a rude approximation to the truth. 
|| See last Report, p. 225. Mahlmann, p. 77. 
