48 REPORT—1840. 
an instrument at high temperatures with that of an air pyrome- 
ter*, and at very low temperatures obtained by means of M. 
Thilorier’s happy discovery of the solidification of carbonic acid 
with air and alcoholt. 
29. MM. Becquerel and Breschet have employed the same 
method for the determination of the temperature of water at 
great depths by sinking the experimental junction of the wires. 
As may be supposed, however, in such cases, great attention is 
requisite to prevent the slightest chemical action, which would 
develope its proper current. They made their observations on 
the Lake of Genevaf. 
30. The same ingenious experimenters have applied this me- 
thod of measuring temperature to the living animal fibre, by 
thrusting a compound needle into the muscular tissue, and with 
very curious results§. M. Dutrochet has lately applied the 
same method to ascertain the proper temperature of plants, a 
yet far more difficult inquiry||. His experiments haye been 
fully corroborated by MM. Van Beek and Bergsma]. 
31. I have applied M. Peltier’s apparatus for the very obvious 
purpose of checking the zero point of thermometers sunk in the 
ground to such a depth that their scale can never be re-examined. 
For this purpose, along with a thermometer 24 French feet 
long**, I sunk a thermo-electric pair of iron and copper, com- 
pletely defended in all its length with a casing impervious to 
water, and its indications have been generally satisfactory. I 
had hoped that, by the use of wires of sufficient thickness, the 
thermo-electric current might be communicated from great 
depths. From experiments which I have made, I am inclined 
to think that their use must be very much limited in this respect, 
on account of the rapidity with which the energy of the circuit 
* Comptes Rendus (Paris), iii. 782. 
+ Ibid, i. 513. Professor Muncke, of Heidelberg, has investigated with 
great care the law of dilatation of alcohol, and the result gives for ordinary 
atmospheric temperatures, a value very sensibly different from the mean dilata- 
tion commonly received from Dalton’s experiments. He has also given the 
result of several series of observations on other fluids, and given formule of ex- 
pansion for each.—Petersburg Transactions—Paper read 5th Sept. 1834. M. 
Rudberg has re-examined the expansibility of dry air and gases (Poggendorfi’s 
Annalen), and he finds an expansion of only 364 or 365 between freezing and 
boiling water instead of °375, as was given very nearly both hy Dalton and Gay 
Lussac. ‘The scientific world will, no doubt, hesitate a little to adopt the new 
determination of this important element, even with all possible respect for M. 
Rudberg’s known skill as an experimentalist. 
+ Bibliotheque Universelle, Nouvelle Série, vii. 173 (1837). 
§ Comptes Rendus (Paris), i. 28, iii. 771. 
|| Ibid, viii. 695, 741, 907. ix. 613. Temp. of Insects, ix. 8]. 
q Ibid, ix. 328. * #** See below. Art. (96.) 
