REPORT ON METEOROLOGY. 
248 
sounding name of the Psychrometer *. This instrument has been 
employed by Baron Humboldt in his recent journey in Asia, 
where he had occasion to observe a very high degree of dryness, 
the coolness by evaporation amounting to 11°* * § 7 cent., the tem¬ 
perature of the air being 23°' 7f. It were to be wished that, 
for the improvement of the theory of the instrument, he had 
at the same time ascertained the dew-point by experiment. 
M. Auguste is himself the author of the formula by which the 
tension of vapour is deduced. He has published not only a 
paper expressly on this subject J, but an essay (which I have 
not been able to meet with,) upon the progress of Hygrometry 
in modern times §. 
The perfection of the method of the moistened thermometer 
forms an important and an interesting problem. Mr. Leslie’s 
solution, which was the first, offers a near approximation to 
the truth, but at the higher temperatures will require modi¬ 
fication, especially as instead of adopting any of the Tables of 
the force of vapour now in use, he has contented himself with 
the general result of some original experiments, that the u capa¬ 
city of air for moisture,” to use his own phrase, is doubled by 
the increase of temperature by every 15° of the centigrade scale. 
This leads him into inevitable errors at higher temperatures||. 
Dr. Anderson’s elaborate investigation contained in an able 
article on Hygrometry in the Edinburgh Encyclopaedia ,to which 
we can do no more than allude, appears also to be faulty in the 
higher parts of the scale, if we can depend upon some ex¬ 
periments recently made by an anonymous writer in India 
Undoubtedly the most valuable application of Professor Leslie’s 
hygrometer will be, by rendering it self-registering on the 
simple principle proposed by the Rev. Mr. Gordon, which is 
similar to that of Rutherford’s minimum thermometer**. 
* Bulletin des Sciences Mathematiques, vii. 379. 
f Fragments Asicitiques, ii. 378. At Geneva, in August last, I observed a 
coolness by evaporation amounting to 20° Fahr., the thermometer in the shade 
being at no less than 92°. I then found it quite impracticable to obtain a de¬ 
position upon Daniell’s hygrometer.— Dec. 1832. 
t Poggendorff’s Annalen, 1828. There is a paper by Brouwer upon Auguste’s 
instrument, in the Amsterdam Journal, entitled “ Bijdragentot de Naturkundige 
Wetenschappen 1831, p. 272. See also Bull, des Sci. Math. x. 302. 
§ In German. Read to the Society of German Naturalists in 1828. 
|| Professor Leslie’s researches are contained in a tract upon “ Heat and 
Moisture,” Edin. 1813 : and in the article Meteorology in the Supplement to 
the Encyclopaedia Britannica. 
See two clever papers in a periodical work entitled “ Gleanings in Science ,” 
Nos. II. and III. Calcutta 1829. The Author points out the great difficulty of 
using Daniell’s'hygrometer in warm climates, from the deterioration of ether. 
** Edinburgh Encyclopaedia, Art. Meteorology, 
Q 2 
