REPORT ON METEOROLOGY. 
225 
the observations of Duperrey, is somewhat less. The tempera¬ 
ture, as it varies with depth, is of course amenable to the laws 
of the maximum density of water ; though with respect to salt 
water, this phenomenon still requires elucidation Within 
the tropics, the temperature constantly diminishes as we de¬ 
scend. Towards latitude 70° this decrease vanishes, and an 
opposite series of phenomena take place ; the temperature in¬ 
creasing as we descend. As these points, though interesting in 
a high degree, are not so intimately connected with Meteoro¬ 
logy as those we have been discussing, and those which yet re¬ 
main, we shall merely give references to those works where 
general views have lately been given on the temperature of the 
sea:—Arago, Annuaire pour 1825; Humboldt, Relation Hi- 
storique , iii. 514—530, and FragmentsAsiatiques, ii. 556; Pou- 
illet, Flemens de Physique , ii. 684; Recent Observations by 
M. Lens, who accompanied Kotzebue; PoggendorfF’s Antialen , 
1830 ; and the Voyages of Reechey and Duperrey. 
From the great and universal importance of the subject of 
Temperature, and the more general views which admit of being 
taken of it, we have been induced to extend our review of its 
different branches to a greater length than we can permit our¬ 
selves in the remainder of the subjects which are before us. 
We proceed therefore to give a brief view of the subject of 
Atmospheric Pressure. 
Notwithstanding the beauty of the Torricellian method, the 
barometer must be admitted to be far from that? state of con¬ 
stancy, simplicity and perfection, which could be wished, for the 
purposes to which it is now applied. My attention has long 
been greatly devoted to the improvement of this instrument, 
and to the careful study of its desiderata ; but I believe we must 
be content to admit, that on every plan which has yet been 
proposed, and with any modification of such plans, the barome¬ 
ter will remain liable to considerable objections. 
Whilst a barometer is immoveably fixed, its capability of pre¬ 
cision is much greater then when it is constructed with a view to 
portability ; indeed there is not perhaps a more difficult problem 
in philosophical mechanism than a satisfactory portable baro-^ 
meter. I have lately had occasion most particularly to consider 
the construction of the instrument in both forms, having last 
year been requested by the Royal Society of Edinburgh to give 
designs for, and order a standard barometer to be placed in 
* From Erman’s experiments it would appear that sea water has no point of 
greatest density above its freezing point. Annales de Chimie, xxxviii. 287. 
P 
