312 GEOGRAPHY AND ASTRONOMY. ing to problem II. And thereby you may find the latitude of any place by problem VII. IXth Use. If you have a broad smooth board with a foot behind at the bottom, to make it stand, such as is described in problemXXIII. of the XIXth sect. and if it be made to stand perpendicular on a horizantal plane by a line and plummet in the middle of it, you may set the bottom or lower edge of this board in the meridian line, and by your eye fixed at the edge of the board and projected along the flat side, you may determine at night, what stars are on the meridian ; and then by the globe (as in problem XXXIII. and XXXIV. section XIX.) or by an instrument called a nocturnal; you may find the hour of the night, or by an easy calculation as in the XXXIIId. problem of this XX. section. ProblemXXXI. " How to know the chief stars, and to find the north pole." If you know any one star you may find out all the rest by considering first some of the nearest stars that lie round it, whether they make a triangle or a quadrangle, straight lines or curves, right angles or oblique angles with the known star. This is easily done by comparing the stars on the globe (being recti- fied to the hour of the night) with the present face of the hea- vens, and the situations of the stars there, as in problem XXXII. section XIX. And indeed it is by this method that we not only learn to know the stars, but even some points in the heavens where no star is. I would instance only in the north pole, which is easily found, if you first learn to know those seven stars which are called Charles' Wain, see figure xxx. four of which in' a quadrangle mayTrepresent a cart or waggon b, r, c, d, and the three others re- presenting the horses. Note also that the star a is called Alioth, d is called Dubbe, b and r are called the two guards or pointers, for they point di- rectly in a straight line to the north pole p, which now is near 24 degrees distant from the star s, which iscalled' the north pole star. You may find the north pole also by the star Alioth, from which a straight line drawn to the pole star s, goes through the pole point p, and leaves it at 24 degrees distance from the pole star. You may find it alsó by the little star n, which is the nearest star to the pole star s ; for a line drawn from n to s is the hy- pothenuse of a right-angled triangle, whose right angle is in the pole point p. ProblemXXXII. " To find the latitude by any star that s on the north meridian." It has been already shewn in the Xth problem of this sec-
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