1 -in:; ih
-in''
278 ArPENDix.
bore tlie unpretending title of an " Essay towards a first approximation
to a Map of Cotidal Lines;" but however lightly the author
might esteem it, there can be no doubt that it tended to remove a
cloud -«'hich hung over numerous difficulties ; and to enable us not
only to take a general view of them, but to see how we shoidd direct
our course in order to attain some knowledge of their intricacies.
In 1831 Mr. Lubbock called the attention of mathematicians, as
well as of practical seamen, to the subject of Tides : but it was Mr.
Whewell who aroused general interest; and, assisted by the Admiralty,
engaged the co-operation of obser\'ers in all quarters of the
globe.
At the first perusal of Mr. Whewell's essay, I was particularly
struck by the following passages : " But in the meantime no one
appears to have attempted to trace the nature of the connexion
among the tides of the different parts of the world. We are, perhaps,
not even yet able to answer decisively the intjuiry which
Bacon suggests to the philosophers of his time, whether the high
water extends across the Atlantic so as to affect, contemporaneously,
the shores of America and Africa ? or, whether it is high on one side
of this ocean when it is low on the o t h e r a t any rate, such observations
have not been extended and generalized." * Also : f
" If the time of high water at Plymouth be five, and at the Eddystone
eight (as formerly stated), the water must be falling for three
hom-s on the shore, while it is rising at the same time at ten or
t«'elve miles distance ; and this through a height of several feet. We
can hardly imagine that any elevation in one of the situations, should
not be transferred to the other in a much shorter time than this.
" There is, in fact, no doubt that most, or all the statements of such
discrepancies, are founded in a mistake arising from the comparison
of two different phenomena; namely, the time of high-water, and
the time" of the change from the flow to the ebb current. In some
cases the one, and in some the other of these tunes, has been
obser\-ed as the time of the tide ; and in this manner have arisen
such anomalies as have been mentioned." And again : {
" The persuasion that, in waters affected by tides, the water rises
while it runs one way, and falls while it runs the opposite way, though
wholly erroneous, is very general."
These, and other valuable remarks, showed me what indistinct or
erroneous ideas I had entertained ; and that many other seamen had
• PhilosophicalTransaotions, 1833, p. 148. t Ibid. 157. I Ibid.
a t p e h d i x .
been simUarly perplexed, I could hare Uttle doubt, ha^-mg of en
i l e d to exiLlene'ed practical men on d>e -bject . « l y ^ U e
expressions 'ride and half-tide,' • tide and quarter-ride, &c„ con
v e U more cUstinct ideas to their minds, than to mme: for to me
thiywere unsatisfactory, and although quite aware of the.r meo^g^
I never bleed them. From 1833, I and ^ ^^^^^^
the Beagle paid more attention to the subject, and rnade obser-
™ i o n i t tlfe manner suggested by Mr. WheweU as often as on
other avocations allowed. Itwas. however,
in the subject, anddLseover difficulties, facts rrreconcUeable to theo^^
without t U g to think how to account for them-unquahf ied even
: I knew V e l f to be for such a task.* Perhaps I was encour^ed
to meditate by Mr. m ewe l l ' s concluding paragraph; t and. separated
from assLance, I tried to reason my way out of the .Memma,
C the help of such few data as I could dwell upon w.th certainty.
. Among the points which I could not establish in my o ^ i ^ V
honrs"(p 167.) " That the tide-wave travels along th,s coast {American)
i ; r n f r t h to south, employing about twelve hours in - t ^ - „ o n f^m
Acapulco to the Strait of Magalhaens." (p. 194 ) " From th c o ^
tiveLrrowness of the passage to " '
certain that these tides must come from the southern s.de of the con^
rent " (p 200.) " The derivative tide which enters such oceans (North
and South Pacific) from the south-east, is diffused o ^ r so w,de a space,
that its amount is also greatly reduced." (p. 217-) &c.
+ " I cannot conclude this memoir without agam expressmg my entire
CO viction of its very imperfect character. I should regret -ts Pubhca^^n,
if T supposed it likely that any inteUigent person could consider t oAerwise
Zn as an attemptto combine such information as we have, and to
point out the want and the use of more. I shall neither be surprised nor
mortified, if the lines which I have drawn shall turn out to be, m many in-
I t c e s , ; ide4 erroneous : I offer them only as the simplest mode w^ich
I can now disLver of grouping the facts which we possess. The lines
which occupy the Atlantic, and those which are near the coasts of Europe,
appea" o have the greatest degree of probability. The tides on th
coL^s of New Zealand and New Holland, have also «consistency which
makes them very probable. The Indian Ocean is less certain ; though
it is not easv to see how the course of the lines can be very widely diffe