11 
relation of temperature to depth which had been observed in the cruise of 
1869 in the North Atlantic basin, the only difference being that the stratum 
of intermixture between the upper warm and lower cold current was about 
150 fathoms deeper off the coast of Portugal than off the coast of Ireland. 
The investigations in the Mediterranean, however, showed that at no depth 
in that inland sea, which was cut off from the general system of polar 
and equatorial oceanic circulation, was there a lower temperature than 55° 
Fahrenheit. 
The author then gave a short account of the experiments conducted by 
himself. Many analyses of the gases dissolved in sea water had been made, 
the results of which shewed, (1) that the agitation of the surface water by 
the steamer's paddles did not, as was at first supposed, tend to aerate the 
water and replace the excess of carbonic acid by oxygen ; (2) that in every 
other respect the results arrived at in 1869 as to the great excess of 
carbonic acid and corresponding deficiency in oxygen in "bottom" waters, 
and the relation of this with the amount of animal life on the sea bottom, 
were confirmed; and (3) that comparing the waters of Southern latitudes 
with those of more Northern ones, both bottom and surface waters 
contained more carbonic acid and less oxygen in the latitude of Portugal 
than in that of Ireland. One instance was given of water from 1065 
fathoms depth, which contained 2.8 volumes of gas in 100 of water, the 
composition of which was 
Carbonic Acid ... ... 53 per cent. 
Oxygen ... 12 „ 
Nitrogen ... ... 35 „ 
The Author had been specially engaged, however, in determining, 
according to a method suggested by himself as applicable for use on board 
ship and also admitting of great accuracy, the amount of chlorine in 
various specimens of sea water, with a view to compare the North 
Atlantic basin with the Mediterranean in this respect. 34 samples were 
examined with the following result expressed in grammes of chlorine per 
1000 cubic centimetres of water. 
Surface Water. Intermediate "Water. Bottom Water. 
12 Samples. 10 Samples. 12 Samples. 
Average 19.94 19.85 19.75 
Maximum ... 20.19 19.94 19.98 
Minimum ... 19.81 19.70 19.46 
These results appear to shew that there is a slight excess of chlorine, and 
therefore of salts generally, in the surface water, attributable probably to 
