Page:Philosophical Transactions - Volume 002.djvu/37

 with it. By this means, the variation may be had well enough to degrees, half degrees, and some smaller parts; and if carefully and curiously prosecuted, even to Minutes too. But it will not be amiss, to do it both by the Sun and Stars, that the greater certainty may be attained.



He Dipping-Needle is to be used at least as Frequently as the former Experiment is made, and in the same places, in order to the same purposes. All that needs be said of the Manner, is, that when the Dipping of the Needle is to be examined, the Circle, in which it moves, is to be hung perpendicular, and turned, till it be just in the Magnetical Meridian, where it dippeth most, and the degree of its depression under the Horizon is to be noted in a Table. See Figure 1.

He Particulars here to be regarded, are, 1. The precise times of the beginnings of the Flood and Ebb, in all Rivers, Bayes, at Promontories, Capes, and in all Roads, Harbours, &c. 2. Which way Currents run in all places, with their Times, Changes, &c. 3. What perpendicular Distance there is, between the highest reach of the Tide, and lowest of the Ebb, both of all Spring-Tides and Neap-Tides, with their irregularities, &c. 4. What day of the Moon's age, and what times of the Year the highest and lowest Tides fall out: And all other considerable Accidents observable in Tides, chiefly in and near all Sea-ports, Harbours, Roads, Islands, &c. as St. Helens Island, Bermuda. 5. The position of the Wind at every Observation of the Tides, &c. 4. To