Page:Philosophical Transactions - Volume 001.djvu/59

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about it, that there is yet another irregularity in the Tides, which never fails, and is no less extraordinary, than what I have been mentioning: which is, that, whereas between the Vernal and Autumnal Equinoxes, that is, for six Moneths together, the Course of irregular Tides about the Quartermoons, is, to run all day, that is, twelve hours, as from about 91/2 to 91/2, 101/4 to 101/4 &c. Eastward, and all night, that is, twelve hours more, Westward: during the other six Moneths, from the Autumnal to the Vernal Equinox, the Current runs all day Westward, and all Night Eastward.

Of this, though I had not the opportunity to be an Eye-witness, as of the other, yet I do not at all doubt, having received so credible Information of it.

To penetrate into the Causes of these: strange Reciprocations of the Tides, would require exact descriptions of the Situation, Shape, and Extent of every piece of the adjacent Coasts of Eust and Herris; the Rocks, Sands, Shelves, Promontorys, Bays, Lakes, Depths, and other Circumstances, which I cannot now set down with any certainty, or accurateness; seeing, they are to be found in no Map, neither had I any opportunity to survey them; nor do they now occur to my Memory, as they did some years ago, when upon occasion I ventured to make a Map of this whole Frith of Berneray, which not having copied. I cannot adventure to beat it out again.

Monsieur Azout's judgment touching the Apertures of Object-glasses, and their Proportions in respect of the several Lengths of Telescopes.

This Author, observing in a small French Tract lately written by him to a Countryman of his, Monsieur L'Abbe Charles; That great Optick Glasses have almost never as great an Aperture as the small ones, in proportion to what they Magnifie, and that therefore they must be more dim; takes occasion to inform

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