96 REPORT— 1840. 
167. Spasky* has taken the trouble to ascertain whether the 
constants in Dulong’s formula (viz. the factor of ¢ and the ex- 
ponent), might not be altered so as to represent the observations 
better, but he has obtained a very insignificant change. 
168. Egent, writing on the same subject, criticises the different 
formula, and gives one expressing the temperature in a series 
of successive powers of logarithms of the force or pressure. 
169. Biot ¢, Schmeddink §, and Roche ||, have all written on the 
same subject recently, and proposed new formule. Mr. Russell 
has proposed to adopt a modification of Dalton’s scale of tem- 
perature, by which the elasticities may follow an accurately 
geometrical progression. Mr. Lubbock** has deduced, from 
theoretical considerations, a formula sufficiently simple, and 
which represents, with extraordinary fidelity, the observations 
of the Commission of the Institute; less accurately those of 
Southern below 212°. 
170. I mention these results as generally connected with the 
subject; the actual range of hygrometric observations requires 
such a formula to be used as shall best represent the elasticities 
under 212°. . 
171. The formule in use are (1.) that derived from the obser- 
vations of Dalton and Ure; (2.) that deduced by Kamtz from his 
own observations ff ; (3.) the table calculated by Ivery’s formula, 
founded on Ure’s experiments ; it is that given in the second 
edition of Daniell’s Meteorological Essays, and adopted in the 
Royal Society’s Instructions for the Antarctic expedition. Of 
these, Dalton’s has best stood the test of time. Kamtz’s is 
recommended by Kupffer{{, but is condemned by Egen§§, 
Lloyd |||], and Apjohn. In the first place, let us turn for a 
moment to the data of the problem. 
172. The dew-point being obtained by the method of Dalton, 
or that of Daniell, the quantity of vapour in the air, and the 
ratio of the contained vapour to what might be contained in 
* Poggendorff, xxx. 351. Instead of e=(1-+ 0°7153 #)°, he finds 
(1 + 719 ¢)*-9987 for the elastic force, ¢ being in cent. degrees. 
+ Pogg. xxvii. 9. t L’Institut, No. 26, p. 222. Pogg. xxxi. 42. 
§ Pogg. xxvii. 40. || Silliman’s Journal, xxvili. 363. 
{ Proceedings, Royal Society of Edinburgh, vol. i. p. 227. 
** On the Heat of Vapours, p. 7. Lond. 1840. 
++ M. Kamtz’s first work on the subject was published at Halle in 1826. In 
the first volume of his Meteorology, p. 289, he has given an account of 
original experiments on which his formula is founded, which appears to differ 
very sensibly from the results incommon use. This formula has had its con- 
stants more lately modified, as appears by M. Kupffer’s citation of it. See 
below. 
tt Bulletin de l’ Acad. de St. Petersbourg, tom. vi. No. 22. 
§§ Pogg. xxvii. 25. || || Proceedings, Royal Irish Academy, 1840. 
