244 
SECOND REPORT -1832. 
The researches of Gay-Lussac upon the scale of Saussure’s 
hair hygrometer, are too well known to require notice here ; we 
only mention them to observe that the analogy to the abscissas 
of a hyperbola, of the tensions of vapour, the ordinates represent¬ 
ing the degrees of the hygrometer, has been further extended 
by Signor Melloni in a long paper recently published on this 
subject*. 
The hygrometer proposed by M. De la Rive indicating the 
temperature evolved by the combination of a film of sulphuric 
acid with the moisture of the atmosphere, has not as far as we 
know come into general use. 
The distribution of vapour in the atmosphere is a most 
curious and difficult problem, of which the data are only now 
beginning to be collected. We know the mean tension of 
vapour at very few points on the surface of the globe, which, 
from the influence of temperature, varies exceedingly, and 
will one day be the subject of connected and scientific dis¬ 
cussion as satisfactory as the isothermal lines are at present. 
Dr. Anderson has given some interesting views upon what we 
may believe to be the distribution of vapour from the equator 
to the polesf, and the same subject has been taken up by Mr. 
Daniell in his Essay on the Constitution of the Atmosphere^. 
As to its variation with height, we are almost equally in the 
dark, but we are certain that intense dryness reigns in the 
higher regions of the atmosphere||. The law of decrease is 
probably not a regular progression : it appears probable from 
many circumstances, and in particular from some experiments 
of Captain Sabine, that the dryness is pretty constant for a 
certain height, and then rapidly diminishes. In fact there is 
certainly a stratum of air at the height of from 1 mile to 4 miles, 
which is more frequently saturated with vapour than any other, 
and which constitutes the region of clouds. 
The annual and diurnal variations of temperature produce 
effects in the distribution of humidity, analogous to those which 
we observe in passing from one latitude to another. Even with 
our extremely limited views of the nature and extent of these 
changes, we can trace, with a little care, the influence of the 
great fundamental law of hygrometry, in producing clouds, 
mists, and other phenomena, which, in hilly countries espe- 
* Annales de Chimie, xliii. 39. 
f Article Hygrometry in the Edinburgh Encyclopedia. 
% Meteorological Essays, p. 73, &c. 
|| The interesting researches of M. Kamtz in the higher Alps, promise to 
throw the greatest light on this important point. I had the satisfaction of wit¬ 
nessing last summer along with him, at the height of 8,500 feet, a degree of 
natural dryness unexampled, I believe, in the annals of hygrometry.— Dec. 1832. 
