296 SIR JAMES C. ROSS ON THE PRESSURE OF THE ATMOSPHERE, ETC. 
Postscript. 
When this paper was drawn up some years ago I was ignorant of the researches of 
M. Daussy on the same subject, or the confirmation of his discovery by Sir John 
Lubbock, whose valuable treatise on the Tides having been long out of print is, 
unfortunately, too little known to naval officers. Dr. Whewell directed my atten- 
tion to it when I mentioned to him the result of my deductions from the observations 
at Port Leopold, and although the investigations of these eminent philosophers relate 
only to the effect of the pressure of the atmosphere on the height of high water, and 
differ widely in their results, owing to the localities in which the observations were 
made being unfavourable for the detection of the universal law which governs the 
amount of apparent irregularities, I have extracted from Sir John Lubbock’s work 
a paragraph which clearly shows the exact state of the question previous to my 
investigations. He says, p. 48, “ M. Daussy has ascertained that at Brest the height 
of the high water varies inversely as the height of the barometer, and that the British 
Channel there rises more than 8 inches for a fall of about half an inch in the baro- 
meter. I have found that at Liverpool a fall of a tenth of an inch in the barometer 
corresponds to a rise in the River Mersey of about an inch, and that at the London 
Docks a fall of one-tenth of an inch in the barometer corresponds to a rise in the 
River Thames of about seven-tenths of an inch. So that with a low barometer the 
tides may be expected to be high, and vice versa coeteris paribus .” 
Thus M. Daussy found the height of high water to be affected 
At Brest in the ratio of 1:16 
Sir John Lubbock at Liverpool . . . 1:10 
And at London 1:7 
The results of their investigations at these three places differed so much from each 
other, that their practical application became limited to the correction of the height 
of high water at the places where the observations were made. 
The result of the deductions from the observations at Port Leopold is, I have no 
doubt, of more universal application in all harbours where the ocean has free ingress 
and egress, as a comparison with the extensive series of tidal observations made at 
New Zealand, Cape Horn and the Falkland Islands, during my voyage to the Antarctic 
Seas in 1839 to 1843, tends to show. But the subject is well worthy of investigation 
in other localities, as doubtless a different ratio will be found to obtain in proportion 
as the ingress of the waters of the ocean is free, or obstructed by narrow channels 
or sand-banks. 
J. C. R. 
Aston- Abbott's House, Aylesbury , 
November 6, 1854. 
