of Edinburgh , Session 1876-77. 
283 
3. Note on Clapeyron’s Formula. By Professor Dewar. 
4. Note an the Specific Gravity of Ocean Water. By 
J. Y. Buchanan. 
During the cruise of the Challenger the specific gravity of the 
surface water was observed daily while at sea, and that of water 
from the bottom and intermediate depths as often as opportunity 
offered. These observations were almost entirely confined to the 
region between the parallels of 40° N. and 40° S. latitudes, which, 
including as it does the regions of the equatorial calms, of the 
trade winds, and to a certain extent of both the northern and 
southern westerly winds is decidedly the most interesting field for 
such investigations. Many valuable observations have been made 
by other observers, and I have availed myself more especially of 
the series of observations made by Lenz during Kotzebue’s voyage 
to the Pacific and back. His observations were almost entirely 
confined to the surface water. 
The density of sea water depends on the amount of salt which it 
contains, on its temperature, and on the pressure to which it is 
subject. Away from the disturbing influences of the shore, the 
water of the ocean is subject to comparatively slight variations in 
saltnesss, so slight indeed that different waters may without 
sensible error be assumed to be equally affected by changes of tem- 
perature and pressure. As the remarks which are offered in the 
present paper have reference to the salinity or concentration of 
the water, the specific gravities have all been reduced to their 
value at 60° F., the unit being that of distilled water at its tem- 
perature of maximum density. The pressure is that of one atmo- 
sphere. 
There are two meteorological causes which affect the saltness of 
the sea; the one is the formation of vapour and the precipitation of 
it as rain, and the other is the freezing of the water and melting of 
the ice thus formed. Vast quantities of solid matter, chiefly car- 
bonate of lime and silica, are removed from the water by living 
organisms, and these substances form the chief components of the 
solid matter brought down in solution by rivers. Although this is 
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