SEA. 
used it was fastened to the deep sea- 
line, just above the lead, so that all the 
way as it descended, the water had a free 
passage through it, by means of the valves 
which were then both open ; but the instant 
it began to be drawn iip, both the valves 
closed by the pressure of the water, and of 
course the thermometer was brought up in 
a body of water of the same temperature 
with that it was let down to.’ With this 
instrument, which is much the same with 
one formerly described by Mr. Boyle; in 
his observations about the saltness of the 
sea, water was fetched up from different 
depths, and its temperature accurately no- 
ticed, in different seasons and latitudes. 
“ August 27, 1772; south latitude 24“ 
40'. The heat of the air was 72j, of the 
vvater at the surface 70, of water tfom the 
depth of 80 fathoms 68. 
“ December 27, 1772, south latitude 58“ 
2l'. Tlie heat of the air was 31, of the wa- 
ter at the surface 32, of water from the 
depth of 160 fathoms 33|. 
“ In the voyage to the high northern lati- 
tudes before mentioned; tliey made use of 
a bottle to bring up water from the bottom, 
which is thus described : ‘ The bottle had a 
coating of wool, three inches thick, which 
was wrapped up in an oiled skin, and let 
into a leather purSe, and the whole inclosed 
in a well-pitched canvas bag, firmly tied to 
the mouth of the bottle, so that not a drop 
of water could penetrate to its surface. A 
bit of lead shaped like a cone, with its base 
downwards, and a cord fixed to its small 
end, was put into the bottle ; and a piece 
of valve leather, with half a dozen Slips of 
thin bladder, were strung on the cord, 
which, when pulled, effectually corked the 
bottle on the inside.’ We have here put 
down two of the experiments, which were 
made during that voyage. 
“ August 4, 1773, north latitude 80“ 30'. 
The heat of the air was 32, of the water af 
the surface 36, of water fetched up from 
the depth of 60 fathoms under the ice, 39. 
“ September 4, 1773, north latitude 65“. 
The heat of the air was 66^, of the water at 
the surface 55; of water from the depth of 
683 fathoms, 40. 
“ It appears from all theSe experiments 
that, when the atmosphere was hotter than 
the surface of the sea, the superficial water 
was hotter than that at a great depth; and 
when the atmosphere was colder than the 
surface of the sea, it is evident that the su- 
perficial water was somewhat colder than at 
a considerable distance below it.” 
Sea-water may be rendered fresh by 
freezing, which excludes or precipitates the 
saline .particles ; or by distillation, which 
leaves the salt in a mass at the bottom of the 
vessel. Upon these principles, a mode of 
obtaining a supply of fresh water at sea was 
recommended some years ago to the Admi- 
ralty, by Dr. Irving. It consisted in only 
adapting a tin tube of suitable dimensions 
to the lid of the common ship’s kettle, and 
condensing the steam in a hogshead which 
served as a receiver. By this mode a sup- 
ply of twenty-five gallons of fresh water per 
hour might be obtained from the kettle of 
One of our ships of war. 
The saline taste of sea-water, is chiefly 
derived from common salt which it holds in 
solution. Sea-water is also distinguished 
by a nauseous bitter taste, which is ascribed 
to the animal and vegetable matters which 
are floating in it. This taste has been com 
sidered as in some measure foreign to it, 
for it is only found in the water on the sur- 
face of the ocean, or near the shores. 
Sea-water, taken up at considerable depths, 
contains only saline matters. The specific 
gravity of sea-water varies from 1.027 to 
1.028. Its greater density is owing to the 
salts which are dissolved in it ; and to this 
impregnation also it is owing, that it is not 
frozen till the temperature is reduced nearly 
to 28“. The salts which are chiefly found 
in sea-water, are muriate of soda, or com- 
mon salt, muriate of magnesia, sulphate of 
magnesia, sulphate of lime and soda. The 
quantity of saline ingredients in the waters 
of the ocean varies from ^ to Jj part Mr. 
Kirwan makes the average quantity about 
^ of its whole weight. The quantity of 
saline contents of water, taken up by Lord 
Mulgrave at the back of Yarmouth Sands, 
in latitude 53“, amounted nearly to ^ ; 
while Bergman found the water taken up 
in the latitude of the Canaries, to contain 
about ^ of its weight of saline matter. 
These quantities, however, vary even in the 
same latitude, during rainy and dry seasons, 
near the land, or the mouths of great ri- 
vers. Tiie difference of latitude does not 
seem to make any considerable difference 
in the proportion of saline matter. In lati- 
tude 80“ north, sixty fathom.s under ice, 
sea-water taken up by Lord Mulgfave, 
yielded about ^ ; in latitude 74°, nearly the 
same ; and in latitude 60“, Pages ob- 
tained four per cent, from water taken up 
in latitude 81“, and the same quantity of 
saline matter from water taken up in lati- 
tudes 45“ and 39“ north. In southern lati- 
