SECTION XIX. 283 time, it is good to have ameridian line drawn both in a north and in a south window ; that is, a line pointing exactly to the north and south : Then set up a broad smooth board of 20 or 24 inches high, and 8 or 10 inches broad ; place it perpendicular on the window with its lower edge on, or parallel to the meridian line ; and fixing your eye at the upright nearest edge of the broad, and glancing along the plane face of it, you will'easily observe what stars are on the meridian, either north or south at that time.* Having found what star is on the meridian, rectify the globe for the latitude, and for the sun's place that day ; then bring the' centre of the star which is on the meridian in the heavens to the edge of the brazen meridian of the globe : and the index will shew the time of night, on the north side of the dial among the evening, or midnight, or early morning hours. Note, How to draw a meridian line, see Sect. XX. Problem XXII. &c. ProblemXXXIV. " The azimuth of any known star being given, to find the time of night." The method I just before proposed, will easily find the azimuth, of any star. Set this tall flat board perpendicular on the window, with one end of it upon the meridian line drawn there, so as that your.eye may just see the star in the window by the foot of the board will cross the meridian line in the true angle of its azimuth, or its distance from north to south. - Having found the azimuth of the star, rectify the globe for the latitude, and for the sun's place as before ; rectify it also for the zenith, and bring the quadrant of altitude to the azimuthof the star in the horizon : then turn the globe till the graduated edge of the quadrant of altitude cut the centre of that star, and the index will shew the hour of night upon the dial plate. Note, That if you have a meridian line drawn on a window, you may find by such methods as these when'the sun is in the- meridian, and what is its azimuth at any time. Problem XXXV. " The altitude of a star being given, to find the hour of the night: ' Note, That the altitude of the star must be found by a quad- rant or some such instrument : But remember thatifyou would find the hour by the altitude of a star, you muát never choose a star that is toonear the meridian ; because for almost two hours toge- ther, the altitude varies very little when it is near the meridian. Rectify the globe as before for latitude, zenith and sun's place ; * Note, To set the board perpendicular and convenient it is fit to have a foot made to it behind, that it may stand firm. And let a strait line be drawn from the top to the bottom of the board, through the middle of it, parallel to the sides; Fix also a pin in the upper part of this line, near the top of this upright board, on which hang a thread and plummet, to play loose in a hole near the bot- tom, to keep it perpendicular. Then the thread hanging almost close to the board will direct your eyes to the stars so the'meridian.
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