234 W. Dennis on the Theory of the Tides. 
ArT. XXIV.—On the best Mode of presenting, in a popular form, 
the Theory of the Tides, with suggestions for constructing illustra- 
tive apparatus ; by WiLLIAM DENNIS, Philadelphia, Pa. 
Iv is remarked by Sir J. Herschel that “many persons find a 
strange difficulty in conceiving how they (the tides) are pro- 
duced ;” and Mrs. Somerville goes so far as to say (Physical Sci- 
ences, ©. 13), that among those classed as astronomical problems 
this “is by far the most difficult and its explanation the least sat- 
isfactory.” This latter statement is perhaps rather broad as it 
stands, but if it were limited somewhat, so that the singularity 
of the phenomenon and the importance and familiar interest 
that attach to it and to its effects should be taken into account, It 
would scarcely require further qualification. It can hardly be 
denied that an intelligent comprehension of this subject is rare 
even among those to whom the causes of most natural phenom- 
ena are familiar, while to the great majority of intelligent peo 
ple it is altogether a mystery. It seems, therefore, worth while 
to enquire whether the difficulties complained of have been re 
duced toa minimum, or whether they be not in part owing 0 
defects or errors in the usual mode of presenting the explanation. 
aving had occasion, in the preparation of a new elementary 
treatise on astronomy, to consider this subject attentively, as 
well as to examine the explanations commonly given, 1 have 
been compelled to conclude that no small portion of the obseu- 
rity and perplexity commonly supposed to belong to this sub- 
ject arises from the want of a proper consideration and statement 
of the ocean are raised by the moon’s attraction, 
in many cases, will be that they are lifted up by main strength, 
as it were, the force of gravity being overcome,’ and having no 
where observed any similar effect of the moon’s attraction, he 
cannot conceive how this can be. Nor will it tend in any 0%. 
"gree to lessen his perplexity if he shall see it stated, (as he may) 
ten-millionth part of the force of gravity, and that of the sun 
attraction not even half as great as it. It is therefore imp? fy 
to show, by a preliminary explanation, that the waters ° 
* An idea akin to this must exist, it would seem, in the minds of those yee 
speak of the lateral attraction of the moon at a given place after or age its 
meridian of that place; as if this disturbing force, so minute © 
st, and in respect of this lateral action, so greatly reduced by its very pat: 
ection, or else by the near approach of the place in question to the mean 
could ever produce any appreciable effect whatever in that way. 
a 
