MR. LUBBOCK ON THE TIDES. 
225 
haps, be necessary to introduce a correction depending upon the height of the baro- 
meter, which may amount in the extreme case to nearly two inches at London. 
Another difficulty arises from the influence of the wind, in as much only as it is 
distinguished from that of the atmospheric pressure. This circumstance, and the 
rude nature of the observations, seem to render it very doubtful whether the refine- 
ments to which I have alluded would be attended with much advantage. 
Table XXX. offers a comparison between the moon’s parallax-correction in the in- 
terval and in the height, as deduced from theory and from observation. See Plate XX. 
In order to diminish the irregularities, and to employ the concourse of all the obser- 
vations, I employed the following method : Let & P be the difference of parallax, or 
The parallax — 57'. 
I suppose the parallax correction to be proportional to £ P ; hence the correction for 
parallax 54' = three times the correction for parallax 56', and the total of the abso- 
lute corrections for parallaxes 54', 55', 56', 58', 59', 60', 61' = y X the correction for 
parallax 54'. Whatever be the law of the parallax-correction, it may certainly be 
considered as proceeding according to powers of S P ; and the preceding hypothesis 
amounts to neglecting all the powers except the first. I now employ only the total 
3 
of the corrections deduced from the discussions, and I multiply it by or the equi- 
valent multiplier, in order to have the correction for 54'. The following Table exhi- 
bits the results, which may each be considered as resulting from the average of about 
800 observations. 
Correction for H. P. 54' at London. 
Moon’s 
Transit. 
Interval. 
A. 
Height. 
A. 
Moon’s 
Transit. 
Interval. 
A. 
Height. 
A. 
h m 
0 30 
1 30 
2 30 
3 30 
4 30 
5 30 
m 
- 1-4 
- 2-7 
- 6-1 
-10*7 
— 13-1 
-12-5 
feet. 
-•56 
— ’65 
—■62 
-•80 
-•83 
-•92 
h m 
6 30 
7 30 
8 30 
9 10 
10 10 
11 30 
m 
- 5-0 
+ 1*7 
+ 3-9 
+ 4-3 
+ 2-5 
+ 0-3 
feet. 
—■72 
-•69 
-•67 
— •60 
-•59 
-•49 
The number of observations from which the preceding Table is deduced is so con- 
siderable, that it is impossible, I think, to admit in it any error of consequence. Ac- 
cording to the expression for tan 2 in p. 222, the moon’s parallax-correction in the 
interval is the same for q> = 90 4; 6, only with a contrary sign, and for the height it 
is the same. In the following Table I have endeavoured to detach all such part of the 
moon’s parallax-correction (deduced from the observations) as is consistent with such 
an expression, from the residue, and I have placed in the next column the moon’s 
parallax-correction calculated by Mr. Jones from the expression for tan 2 ^ in p. 222. 
2 G 
mdcccxxxvi. 
