88 THE ATLANTIC. (CHAP. 1. 
lected at every ten fathoms, for the purpose of ascertaining whether 
any effect is produced upon the specific gravity of the upper stratum 
by evaporation, and how far down this effect extends. 
Transparency of the Water.—Observations for transparency should 
be taken at various depths and under different conditions by means of 
Mr. Siemens’s photographic apparatus. As, however, the action of this 
depends upon the more refrangible rays, and the absorption of these 
and of the more luminous rays might be different, and that, in a man- 
ner varying with circumstances, such as the presence or absence of sus- 
pended matter, etc., the transparency of the sea should also be tested by 
lowering a white plate or large white tile to various measured depths, 
and noting the change of intensity and color as it descends, and the 
depth at which it ceases to be visible. The state of the sky at the time 
should be mentioned, and the altitude of the sun, if shining, roughly 
measured, or, if not shining, deduced from the time of day. 
Relation of Barometric Pressure to Latitude.—In Poggendorf’s 
‘“Annalen,” vol. xxvi., 1832, p. 395, is a remarkable paper by Professor 
G. F. Schouw on the relation between the height of the barometer at 
the level of the sea, and the latitude of the place of observation. At 
page 434 is a rough statement of the results of his researches, the 
heights being given in Paris lines. 
Barometer 
Lat. mercury at 0° C. 
On MER ero eno cHAib ote Coole cc mance aoe 337°0 
LO eye teae s, a.upeietaatiait/ sia eee momento eee atte 3375 
Dera Seco, Rare ain in lost Gaetan Ree renee eae ieee 3385 
Orga ce Se ee oe eG FETE TRO IC eee a near 339-0 
A EEPSRIS tae To OSE eRe Pe tea Tash e eet 3380 
BO eat snsde Clad) & Stee a Oe ee wee Se EOE I ote 3370 
(HOSE Sere fen AN Grong ccncao aoeooe He 335°5 
ITE a, One, RANE MERC rae o's oo coe aonere nec 3330 
ie oy Seah asters, Sia ie van nen MLN de Re ee eass tet oe eee 334:0 
UD iaas kOe. ros ENS Ech, hols PAOLO oe ee enereae eos SARL 335'5 
The expedition might contribute to the examination of this law, not 
only by giving especial attention to the barometer observations at 
about the critical latitudes 0°, 30°, 65°, 70°, but also by comparing any 
barometers with which long series of observations have been made at 
any port they may touch at, with the ship’s standard barometer. 
It appears probable from Schouw’s paper that certain meridians are 
meridians of high pressure, and others of low pressure. 
