Note n — BOOK I.

By the Refractive Power of the Air, the Sun, and the other heavenly Bodies seem higher than really they are, especially near the Horizon. What the Refractions amount unto, what Variations they have, and what Alterations in time they cause, may be briefly seen in a little Book called, The Artificial Clock-Maker, Chap. 11.

Although this inflective Quality of the Air be a great Incumbrance and Confusion of Astronomical Observations;——yet it is not without some considerable Benefit to Navigation; and indeed in some Cases, the Benefit thereby obtained is much greater than would be the Benefit of having the Ray proceed in an exact straight Line. [Then he mentions the Benefit hereof to the Polar Parts of the World.] But this by the by (saith he.) The great Advantage I consider therein, is the first Discovery of Land upon the Sea; for by means hereof, the tops of Hills and Lands are raised up into the Air, so as to be discoverable several Leagues farther off on the Sea than they would be, were there no such Refraction, which is of great Benefit to Navigation for steering their Course in the Night, when they approach near Land; and likewise for directing them in the Day-time, much more certainly than the most exact Celestial Observations could do by the Help of an uninflected Ray, especially in such Places as they have no Soundings. [Then he proposes a Method to find by these means the Distance of Objects at Sea.] V. Dr. Hook’s Post. Works. Lect. of Navig. p. 466.