S T A 



"ic2 for the purpose. It \\-ill be necessary here to notice that the esti- 

 mation made with one telescope cannot be applied to those made with 

 another, nor can the estimations made with different powers, though with 

 the same telescope, be applied to each other ; therefore if we would wish 

 to compare any such observations together with a view to see whether 

 a change in the distance has taken place, it should be done with the very 

 same telescope and power, even with the very same eye-glass or glasses, 



In the third class are placed all those double stars that are more than 

 5 but less than 15" asunder. In the same manner that the stars in the 

 1st and 2d classes will serve to try the goodness of the most capital in- 

 struments, these will afford objects for telescopes of inferior power, such 

 as magnify from 40 to 100 times. The observer may take them in this 

 or the like order j Ursae Maj., y Delphini, y Arietis, a- Bootis, y Virgi- 

 nia, / Cassiopeae, p. Cygni. And if he can see all these he may pass over 

 into the second class, and direct his instrument to some of those that are 

 pointed out as objects for the very best teleseopes, where he will soon 

 and the want of superior power. 



The 4th, 5th, and 6th classes contain double stars that are from 15 to 

 SO" ; from 30" to 1', and from 1' to 2' or more asunder. PhiL Tram, vol, 

 72, ':-5. 



For a list of a few of the most remarkable double stars <see Tetefcope. 



