S T A 



. of six inches and a quarter, with a power of 227, and 460 ; when the stars 

 were detected, he used a gradual variety of powers from 460 to 6000. 



These double stars are divided into several different classes. In the 

 first are placed all those which require a very superior telescope, the ut- 

 most clearness of air, and every other favourable circumstance to be seen 

 at all, or well enough to judge of them. Their distance is so extremely 

 small (seldom exceeding two diameters oi the largest) that it cannot be 

 accurately measured by the 'micrometer, but may be more correctly es- 

 timated by the eye in measures of their own apparent diameters. It 

 should be observed, that since it will require no common stretch of power 

 and distinctness to see these double stars, it will .*. not be amiss to go 

 gradually through a few preparatory steps of vision, such as the follow- 

 ing : for instance, when y Coron. Borealis (one of the most minute 

 double stars) is proposed to be viewed, let the telescope be some time be- 

 fore directed to Geminorum, or if not in view to either of the follow- 

 ing stars, Aquarii, p Draconis, g Herculis, a, Piscium, or the curious 

 double-double star t Lyrae. These should be kept in view for a consider- 

 able time, that the eye may acquire the habit of seeing such objects well 

 and distinctly. The observer may next proceed to the | Ursae Majoris, 

 and the beautiful treble star in Monoceros' right foot ; after these to t 

 Bootis, which is a fine miniature of a, Geminorum, to the star preceding" 

 K Orionis, and to n Orionis. By this time both the eye and the telescope 

 will be prepared for a still finer picture, which is >j- Coronae Boreaiis. It 

 will be in vain to attempt this latter, if all the former, at least * Bootis, 

 cannot be distinctly perceived to be fairly separated ; because it is almost 

 as fine a miniature of * Bootis as that is of , Geminorum. To try stars 

 of unequal magnitude, it Avill be expedient to take them in some such 

 order as the following : . Herculis, o> Aurigse, Geminorum, k Cygni, 

 t Persei, and b Draconis j from these the observer may proceed to a most 

 beautiful object t Bootis. As the foregoing remarks have suggested the 

 method of seeing how far the power and distinctness of our instruments 

 will reach, we may next add the way of finding how much light we have 

 The observer may begin with the pole star, and Lyrae, then go to the 

 star south of s Ajquilse, the treble star near k Aquilse, and last of all to 

 the star following o Aquilae. Now if his telescope has not a great deal 

 of good light, he will not he able to see some of the small stars that ac- 

 company them, 



In the second class of double stars ere put all those that are proper for 



estimations by the eye, or very delicate measures of the micrometer. 



To compare the distances with the apparent diameters, the power of the 



telescope should not be much less than 200, as they will otherwise be too 



275 Q2 



