...or W. of the first Meridian. 9. The Visible Horizon is the limit of the observer's view at sea. 10. The Sensible Horizon is a Plane touching the Earth's surface at the place of the observer. NOTE. — This is also called the Apparent Horizon. 11. The Rational Horizon...

...and therefore its parallels at right angles. Secondaries to the celestial equator are hour-circles. To any observer the sensible horizon is a plane touching...the rational horizon, whose poles, zenith and nadir, nre the traces of a vertical line, and whose secondaries are vertical circles. One of the vertical...

...and therefore its parallels at right angles. Secondaries to the celestial equator are hour-circles. To any observer the sensible horizon is a plane touching...the point of observation ; and a plane parallel to tliis plane through the earth's centre traces out on the celestial sphere the rational horizon, whose...

...and therefore its parallels at right angles. Secondaries to the celestial equator are hour-circles. To any observer the sensible horizon is a plane touching...celestial meridian, and passes through his zenith and nadir, and the north and south poles of the celestial sphere ; its plane is the same with that...

...b, c, a : the angles %(fl + y), %(fi — y) are both two valued. ButO<£(/? + r) <'ln, -n<%(ft-y)<n; and together they give only two values each to ft,...celestial meridian, and passes through his zenith a'nd nadir, and the north and south poles of the celestial sphere ; its plane is the same with that...