HOW TO OBSERVE THE HEAVENS. 



335 



Fig. 3. 



By attentively observing for a few successive hours the changes of position ' 

 of these objects with relation to the horizon, it will be easily perceived that 

 the line through the pointers and the pole-star revolves round the latter point 

 as a centre, and in three hours it will be observed to revolve through an angle 

 of 45°, which being half a right angle, can be estimated with some degree of 

 approximation by the eye. We may thus see that the firmament appears to 

 revolve round the axis of the sphere at the rate of about 15° per hour. 



Another remarkable group of stars visible in northern latitudes at all sea- 

 sons, is the constellation called Cassiopeia, consisting of five principal stars. 

 The configuration of these, which is given in the annexed diagram, fig. 4. is 

 familiar to every eye accustomed to contemplate the heavens. The star 0, is 

 of the second, and the remaining four of the third magnitude*. 



This constellation being in the quarter of the heavens opposite to that in 

 which the sun is in the month of October, will be seen on the meridian, or 



