ON WAVES. 419 
cast upon science by the imperfect state of this branch of 
knowledge. That the solar and lunar attractions produced 
some effect upon the tides, every one knew; but the problem 
was far from having been reduced into that condition in which 
it could be said that the phenomena of the heavens being given, 
the tides could be determined in magnitude and in time. So 
perfect, however, has this prediction lately become, that Mr. 
Lubbock has said that, considering how well theory agrees 
with observation, he is not sanguine that any material im- 
provements in prediction will hereafter be made. And, indeed, 
this assurance appears to rest on valid grounds when it is con- 
sidered that the tide tables which have resulted from his re- 
searches, and those of Mr. Whewell, give predictions whose 
errors are within the limits of the errors of observation. 
But although the Cerestra, Mecuantiso of the tides has 
been thus perfectly analysed and explained, there remain a 
great variety of considerations relating to the propagation of 
tides along the surface of the globe which are as yet unex-~ 
plained; these constitute the TeRrestRIAL Mecuanism of 
the tides. It is in the generation only of the tide that the solar 
and lunar attraction produce their effects: over the subsequent 
propagation of them, they exercise little or no influence. It 
is not until 50 or 60 hours after their creation that the tides 
reach our shores, having moved in the interval in every possible 
direction, and with every velocity from 100 to 10 miles an 
hour. This moving elevation of fluid may be conveniently de- 
signated a wave, and its history will be the history of the tidal 
wave ; but to confer upon it the name of wave does not imply 
that its laws are those which belong to any other similar ele- 
vation with which we are acquainted. It was necessary to 
investigate the nature of this tide wave—to examine the 
hydrodynamical mechanism by which it is transferred from one 
place to another,—to determine the laws which regulate its form 
and its velocity—to ascertain if any relations exist between the 
form and dimensions of its bed, and its own form and rate of 
transference. These and many similar points were still un- 
known. Laplace has said, in speaking of these points, “les 
circonstances dont elles dependent, ne sont pas connues.” 
Mr. Lubbock, in reference to the fluctuation of the establish- 
ment, says, “ this perplexing fluctuation presents an insuperable 
obstacle to extreme accuracy in tide predictions until it can be 
explained ; at present we are only left to conjecture respecting 
the cause.”” And similar sentiments are expressed by Mr, 
Whewell in the seventh series of his researches on the tides, 
2E2 
