(313)
which seems to observe this or some such like Proportion; which is supposed still to hold in all Tides, be the Duration what it will; the Increase still continuing proportionably till the very midle of the Hight and Duration, and Decreasing afterwards in the same manner: Which whether it be so indeed or not, is that, which is desired to be known.
There is the like Proportion here supposed to be in the different degrees of the Velocity or the Current of the Water after Equal spaces of Times, as in its Rising and Falling: And so it is markt in the Third Column. But because the true Velocity of the Current of the Water, raised above the Levell 4561000 of a foot, is unknown, it is by way of Supposition set at ten feet in one Minute of an Hour, which being once stated, the rest distant from each other by the space of 20 Minutes of an Hour, are set down according to the same Proportion of Sines[errata 1] before suggested. It being supposed, that if the the Velocity of the Current of the Tide, after it hath flowed 20 minutes 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 will in the like space of Time move 114 f.2761000, 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 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 Royall 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 Clock-work, 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.
