to the same _Proportions_ of _Sines_ before
suggested. It being supposed, that of the _Velocity_ of the Current of the
Tide, after it hath flowed 20 minuts of an hour, be such, as a Log of Wood
placed in the Water will move 10 foot in the space of one minute of time,
at the middle of the Tide it will in the like space of Time move 114 f.
276/1000, and so proportionably at other times: Which, howsoever these
Proportions shall be found by Experiments to fall out, may be not unworthy
of the pains and charges requisite to acquire the knowledge of it. For,
besides the satisfaction it may afford upon other accounts, it may possibly
be of no small use to those, who need an exact reckoning of their Ships
running, when the Velocity of the Current of the Tide may be necessary to
be known; lest through the defect of the knowledge of that, especially when
it is reckoned less than indeed it is, the Ship be thrown in the night upon
Shores, Rocks or Sands, when they reckon themselves to be far from them.

The Numbers in the 4, 5, 6, 7, and 8. _Columns_ are set down at random,
only for _Examples_ sake; there being no difficulty in the apprehension of
it, and imitating of it in setting down the true Hights and Variations of
the _Thermometer_, _Baroscope_, &c. The Use whereof is so vulgarly known,
that there needs no further Direction concerning them. But if any person
who would make these Experiments, do not know the fabrick or use of any of
the Instruments requisite for some of these Observations, nor where to have
them, he may address himself to Mr. _Shortgrave_, one of the _Operators_ of
the _Royal Society_, lodged in _Gresham Colledge_, from whom he will
receive full satisfaction about these things.

But the labour employed in the Observations of the Heat, Cold, &c. required
to be taken notice of in order to the Ends proposed in the former _Tract_,
and others that may be of no less delight than advantage, will be much
retrenched, when Dr. _Christopher Wren_ puts in practice, what he some
years ago proposed to the _Royal Society_ concerning an _Engine_ with a
_Clockwork_, which may perform these Observations in the last enumerate
_Columns_, without being toucht or lookt after but once or twice a day.

The Tables themselves follow,

{314}

_A Perpendicular Line divided into _Signes_, supposed to be the _Periods_
of the Risings and Fallings of the Tides, as is in the other Table
represented._

[Illustration]

1666. Age of