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SIR JAMES C. ROSS ON THE EFFECT OF THE PRESSURE OF THE 
Explanation of Tables A. and B. which follow : — 
From the preceding Tables, the arithmetic mean of the hourly observations of the 
height of the sea for each day is taken as the mean level of the ocean for that day, 
and the mean of the hourly observed heights of the barometer as the corresponding 
mean pressure of the atmosphere ; these mean levels, and corresponding mean pres- 
sures, are brought together in the following Table A., arranged in the order of the 
days of observation. 
In Table B., commencing with the day of greatest mean pressure, they are arranged 
in the order of the mean heights of the barometer, with the corresponding mean 
levels, without regard to the dates of observation, for the purpose of showing the 
dependence the latter have on the former. 
In the diagram of curves which is formed from Table A., the abscissae represent 
the days of the month, from the 1st of November to the end of December 1848; 
the ordinates in the upper half of the diagram the observed mean level of the ocean, 
and in the lower half the corresponding mean height of the barometer on each day 
during that period. 
