TEL 



expected that we see em a er graes sance. ave nown 

 take up two or three months before the eye was sufficiently acquainted 

 with the object to judge with the requisita precision. ( Hersch. Phil. 

 Trans.) 



(9) It is a singular fact, that a double star, where one of them is of Iho 

 last degree of faintness, may be best seen by directing the eye to another 

 part of th-j field. In this way a faint star ia the neighbourhood of a 

 large one will offr'n become very conspicuous, though it will totally dis- 

 .appear, as if suddenly blotted out, when the eye is turned full upon it. 

 The small companion of 23 (h] Urss Maj., is a remarkable instance of 

 this; also P<vsei, 7 Tauri, 43 Persei, ; Leporis. The lateral portions 

 of the rina less faiued b stron lih-! n les x - 



Of the powers necessary for obssrv'ng various celestial ofy'eots. 

 Comets may be advantageously seen with a power of about 15. 

 The sun, moon, and nebula, with powers of from 45 to 60. 

 Jupiter and his moons from 80 to 130 ; but for estimating the brightness 

 and nppareat magnitude of the satellites, a lower power than 18'J should 

 not be attempted. The belts of Jupiter are scarcely discernable ia a cna 



3 

 foot achromatic, but may be seen with an IS inch of 1 aperture, and 



power of 40; and arc easily visible in a two feet, with an aperture of 

 1., with a power of from 30 to CO. Note. The 2d satellite ia consider- 



ably larger than any of the rest; the 1st is a little larger tluiu tlis 2d, 

 and nearly of the size of the 4th. 



Saturn. The best powers for general purposes are from 130 to 200. 

 To view him with effect, ha should not ba more than t\vo, or, in very 

 fine nights, three hours from tha meridian. The phenomena most wor- 

 thy of observation in this planet, are the following : his belts; the sin- 

 gular compression at his poles ; his double ring ; the shadow of the ring 

 upon the planet, and of the planet .upon the ring ; and bis seven satel- 

 lites. The ring- may be seen ia the 18 inch /telescope with a power of 

 40 ; but for observing the division of the ring, its shadow upon the pla- 

 liet, his belts, and the compression at his poles, we should not have a' 

 less power than 200. As to ius satellites, the visibility of these minute 



