m 
THE RELATIVE LEVEL OF LAND AND SEA. 
parallax correction; and stated that the 
result was a remarkable conformity be- 
tween the results of Bernouilli’s theo- 
ry, and the results of observations con- 
tinued for nineteen years at the Lon- 
don Docks. But to render the accord- 
ance as exact as it was found to be 
capable of being it was necessary to 
compare the time of the tide, not with 
that transit of the Moon which imme- 
diately preceded it, but with that which 
took place about five lunar half days. 
To explain this popularly, the learned 
gentleman stated, that however para- 
doxical it might appear to persons not 
acquainted with tlie subject, yet true it 
was, that although the tide depended 
essentially upon the Moon, yet, any 
particular tide, as it reaches London, 
would not be in any way sensibly affect- 
ed, were the Moon at that instant, or 
even at its last transit, to have been an- 
nihilated ; for it was the Moon as it 
existed fifty or sixty hours before, which 
caused the disturbance of the ocean, 
which ultimately, resulted in that tide 
reaching the port of London. The 
learned gentleman then exhibited sever- 
al diagrams, in which the variations of 
the heights of the tide, as resulting 
from calculations founded upon the 
th eory, were compared with the results 
of observations. The general forms of 
the two curves which represented these 
two results, corresponded very re mark- 
ably ; but the curve corresponding to 
the actual observations, appeared the 
more angular or broken in its form, for 
which the learned gentleman satisfacto- 
rily accounted, by stating that the ob- 
servations were neither sufficiently nu- 
merous, nor sufficiently precise, from 
the very manner in which they were 
taken and accorded, to warrant an ex- 
pectation of a closer conformity, or a 
more regular curvature. 'Wiien it is 
recollected that the observations are at 
first written on a slate, and then trans- 
ferred to the written register, by men 
otherwise much employed, and whose 
rank in life was not such as would lead 
us to expect scrupulous care, it was not 
to be wondered at, if occasionally an 
error of transcript should occur, or 
even if the observation of one transit 
was set down as belonging to the next. 
When to these circumstances it was 
added, that the tide at London was in 
all pi'obability, . if not certainly, made 
up of two tides, one having already 
come round the British Islands, meet- 
ing the other as it came up the British 
Channel, it was altogether surprising 
that the coincidence should be so exact ; 
and it was one among many other valu- 
able results of these investigations, that 
it was now pretty certain that tide ta- 
bles constructed for the port of London, 
by the theory of Bernouilli, would give 
the height and interval with a precision 
quite sufficient for all practical pur- 
poses, and which might be relied on as 
sufficiently exact, when due caution was 
used in their construction, and the ne- 
cessary and known corrections applied. 
In conclusion, Mr. Lubbock said, the 
Observations for the ])ort of London 
had now been continued from the com- 
mencement of this century, and those 
for Liverpool, as we understood, about 
twenty-five years. 
The arrangement of the papers made 
hy the Committee now required the 
President to give a report or the pro- 
ceedings of the Committee appointed 
hy the Association to fix the relative le- 
vel of land and sea ; the chair was there- 
fore taken by Sir David Brewster, one 
of the Vice Presidents, and Mr. Whe- 
well presented himself to the Section. 
He commenced by saying, that as in 
the discussion of the relative level of 
land and sea, the tides of the ocean 
were an important element, he should 
preface the remarks upon that subject, 
which he intended to submit, by mak- 
ing a few observations upon the very 
valuable communication of his friend 
Mr. Lubbock. The communication hs 
highly eulogized, and pointed out to 
the Section the importance, of many of 
the conclusions, should they prove here- 
after to be generally applicable : but he 
expressed strongly his fears that this 
would not be the case. Observation- 
had, in the instance of the tides, far 
outstripped theory, for many reasons, 
which it w'ould be imposible to detail; 
but among the most prominent wero 
the complexity of the problem itself in- 
volving the astronomical theories both 
of the Sun and Moon the masses of 
these bodies; the motions of disturbed 
fluids, and local causes, tending to alter 
or modify the general geographical ef- 
fect of the great tidewave at any parti- 
cular place. It was upon a careful re- 
view of these considerations, that he 
was led to fear that it would be still 
many years before theory would be- 
