ASTRONOMICAL INSTRUMENTS. 



177 



In Tycho's edition of this instrument there is first a large 

 circle, EEC, fixed in the plane of the meridian, having its poles, 

 D c, pointing to the poles of the heavens ; inside this there is 

 another circle, F i H, turning on the pivots D c, and carrying fixed 

 to it the circle o P, arranged in a plane at right angles to the points 



ZODIACALE& 



i K, which are placed at a distance from c and D equal to the 

 obliquity of the ecliptic ; so that i and K represent the poles of 

 the ecliptic, and the circle o P the ecliptic itself. There is another 

 circle, R M, turning on the pivots i and K, representing a meridian 

 of longitude along which latitude is measured. 



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