ave
a whole series of minor disturbances, very like those discussed in No.
7, under the lunar theory, but more complex still, because there are two
perturbing bodies instead of only one.

The subject of the tides is, therefore, very recondite; and though one
may give some elementary account of its main features, it will be best
to defer this to a separate lecture (Lecture XVII).

I had better, however, here say that Newton did not limit himself to the
consideration of the primary oceanic humps: he pursued the subject into
geographical detail. He pointed out that, although the rise and fall of
the tide at mid-ocean islands would be but small, yet on stretches of
coast the wave would fling itself, and by its momentum would propel the
waters, to a much greater height--for instance, 20 or 30 feet;
especially in some funnel-shaped openings like the Bristol Channel and
the Bay of Fundy, where the concentrated impetus of the water is
enormous.

He also showed how the tidal waves reached different stations in
successive regular order each day; and how some places might be fed with
tide by two distinct channels; and that if the time of these channels
happened to differ by six hours, a high tide might be arriving by one
channel and a low tide by the other, so that the place would only feel
the difference, and so have a very small observed rise and fall;
instancing a port in China (in the Gulf of Tonquin) where that
approximately occurs.

In fact, although his theory was not, as we now know, complete or final,
yet it satisfactorily explained a mass of intricate detail as well as
the main features of the tides.

No. 16. The sun's mass being known, he calculated the height of the
solar tide.

No. 17. From the observed heights of spring and neap tides he determined
the lunar tide, and thence made an estimate of the mass of the moon.

Knowing the sun's mass and distance, it was not difficult for Newton to
calculate the height of the protuberance caused by it in a pasty ocean
covering the whole earth. I say pasty, because, if there was any
tendency for impulses to accumulate, as timely pushes given to a
pendulum accumulate, the amount of disturbance might become excessive,
and its calculation would involve a multitude of data. The Newtonian
tide ignored this, thus practically treating the motion as either
dead-beat, or else the impulses as very inadequately timed. With this
reservation the mid-ocean tide due to the action of t