294 
SIR JAMES C. ROSS ON THE EFFECT OF THE PRESSURE OF THE 
the ocean on the corresponding days, and from the difference of the pressures and 
the difference of the levels to determine the relation of each to the other. 
inches. ft. in. 
The mean of three days’ greatest pressure was 30’ 227 Of corresponding level 20 8*4 
The mean of three days’ least pressure was 29*559 Of corresponding level 21 5*4 
Difference ‘668 Difference 9‘0 
Thus a difference of pressure equal to '668 of an inch in the barometer, produces 
* 
a difference of 9 inches in the mean level of the ocean, from which we can of course 
readily compute the exact relation of cause and effect. Thus the difference of level, 
9 inches, divided by the difference of pressure 0‘668 of an inch, equals 13*467. The 
effect, therefore, of the pressure of the atmosphere on the level of the ocean is 13'467 
times greater than the effect it produces on the mercury in the barometer, or very 
nearly in the inverse ratio of the specific gravity of the two bodies ; that of the sea- 
water being 1'026, and that of mercury 13*566, or as 1 to 13*224. 
This remarkable coincidence of the results must, however, in this case be con- 
sidered in a great measure accidental*, for if instead of the three days’ greatest and 
least pressure we were to take seven days of each, from which a better result might 
be expected, we find, instead of the ratio being as 1 to 13*467, it would by these 
means become as 1 to 12*562 ; and if we take the mean of twelve highest and twelve 
lowest barometers, the ratio would be still further reduced as 1 to 11*60; but these 
differences in the result are chiefly caused by the evident irregularities of the mean 
level on the 9th and 20th of November, occasioned by a heavy gale of wind, in each 
case of two days’ continuance. This circumstance, although accounted for in this 
particular instance, seems to indicate the necessity of multiplying observations of this 
nature before exact results can be determined. 
I may here remark, that the effect produced appears from these observations to be 
strictly uniform in its progression from the greatest to the least pressure. By com- 
bining the mean of the three days’ observations of next greater and three days of less 
pressure with that nearest to the mean pressure for the whole period, we find the 
result corresponds nearly with the mean pressure, and the ratio between the ex- 
tremes almost equal ; thus, on December 11, the mean pressure was 29*879, differing 
very little from the mean of the whole period ; and the three days’ observations above 
and below combined with it, give a mean of 29*867, the corresponding mean level 
of the seven days being 21 ft. 0*16 in., which so closely approaches that of the whole 
period, that they may be deemed identical, and would tend to show that the effect 
from the greatest to the mean pressure, and from the mean to the least pressure, is in 
strict progression. It is not possible, however, from so limited a number of obser- 
vations, to determine this point with certainty, or to attempt any intermediate infer- 
ences. 
We have, from these observations, been able to deduce results which plainly 
point to the law which governs the effect of the pressure of the atmosphere on the 
