ASTRONOMICAL INSTRUMENTS. 179 



ingenuity of man had contrived for the observation of the heavenly 

 bodies before the introduction of the telescope. In addition to 

 the Quadrans Muralis and the Armilla to which we have before 

 referred we have the Instrumentum paralldcticum sive Regularum, 

 for measuring altitudes ; the Quadrans Maximus chalibeus quad- 

 rato indusus et horizonti azimuthali chalybeo insistens, the Sextans 

 astronomicus trigonicus distantiis rimandis, and many others. 



All these were much larger than the Greek instruments because 

 increased size of instruments were necessary for increased accuracy 

 of reading. Ptolemy read the divisions on his quadrant, which 



Diagonal Scale. 



was used mainly for observing the height of the sun, by allowing 

 the shadow of a cylinder at its centre to fall on another 

 movable along the divided limb of the instrument. Hipparchus 

 observed within ten minutes of arc. Tycho used plain sights, 

 which were pointed to the object ; the circles were divided to 

 minutes of arc, and by using transversals, or a diagonal scale, a 

 method due to Richard Chanzler, according to Digges (Alee, seu 

 scales. Mathematics, Londini, 1573), the arc was divided down to 

 ten seconds. This method is well seen in the quadrant formerly 

 belonging to Napier of Merchistoun, contributed by the Univer- 

 sity of Edinburgh. 



