MR. LUBBOCK ON THE TIDES. 
221 
westerly winds raise it. As northerly winds raise the barometer and southerly winds 
depress it, it will be difficult, if not impossible, to separate the effect of winds and 
that of the variation in the pressure of the atmosphere from each other. 
I requested Mr. Dessiou to separate and class the errors of the predicted heights 
from Table D., in order to ascertain the variation in the height of high water at 
London simultaneous with the variation of the barometer during 1835. 
Barom. Therm. inches. 
For 29 29 
29- 77 
30- 19 
51-9, mean of 
59-0 
56-9 
68 ' 
282 ' 
351- 
results, we found the mean 
error in the calculated 
heights of high water . . . 
+ 6*1 
+ io-7 
+ 12-4 
so that the water rises 6-3 inches for *90 depression of the barometer. 
I have found on several occasions when remarkably high tides have taken place 
at London, that they have been preceded by a very low barometer. 
If these collateral inquiries relating to the influence of the wind and of the atmo- 
spheric pressure appear of sufficient importance to deserve a complete and satisfactory 
solution, much additional labour must be devoted to the accomplishment of this 
object. I find upon comparing the registers of the London and St. Katherine Docks, 
that the direction of the wind is scarcely ever noted to be the same on the same day; 
probably the direction is always fluctuating, and the discrepancy may then be ac- 
counted for by supposing that the observation is not made at the same moment at 
both places. The barometer admits of more precise observation ; but if the tide 
originates at a very remote distance on the surface of the earth, the atmospheric 
pressure there has probably more influence upon the phenomena than the pressure 
in our vicinity. This difficulty is diminished by the circumstance that the great fluc- 
tuations of the barometer are not rapid, and that the variations in the pressure of the 
atmosphere are extremely extensive. It will still, however, I apprehend, be very 
difficult to distinguish between the effects arising from variations in the atmospheric 
pressure, and those arising immediately from the effect of wind, as I have before re- 
marked. 
When the discussion of the observations of the tides made at Liverpool was pub- 
lished, although the opinion of several persons whom I consulted was in favour of 
apparent solar time having been employed by Mr. Hutchinson in registering the 
observations, I was unable to arrive at any certain conclusion in this particular. 
But by comparing our predicted tides for Liverpool with the observations made there 
in February last, it seems beyond doubt that Mr. Hutchinson did employ apparent 
solar time, and our tables must be interpreted accordingly, for the mean error of our 
predicted times of high water for last February is only three minutes, while the equa- 
tion of time for that month is much more considerable. 
If the surface of the fluid assume the same form at any given instant as it would 
do if the forces then acting upon each particle were invariable in magnitude and 
direction, the variation of the height of the water, or distance of a particle at the 
