438 Saturn's Ring. — Double Stars. — Occultations. 



Dollond, which had T \ inore aperture, and a niost exquisite cor- 

 rection. Secchi, in 1855, with the grand Merz achromatic at 

 Rome, gave it but 0" - 978 of distance, and it must be owned 

 that its aspect is entirely that of mutual connection, but it is 

 generally considered stationary ; and this fact renders it a most 

 useful criterion for instruments of moderate size, as the rapid 

 motion of many test-objects is continually altering their value. 

 £ is the lowermost, and somewhat the brightest of the " crooked 

 row." 



To give the smaller instruments their turn, we will conclude 

 our present section with 



23. 5 Bootis, V 50". 75°. 3| and 8±. Yellow and light 

 blue, or lilac. Wide as this object is, it is pleasing from the 

 contrast of colour. To find it, run a line from Arcturus 

 through s, and carry it nearly as far again. 



OCCULTATIONS. 



The occultation of a considerable star by the moon, espe- 

 cially its disappearance behind the dark limb, when rendered 

 sufficiently visible by the earth-light, is a striking phenomenon. 

 Though the different positions of the moon in the sky, night 

 after night, sufficiently show the rapidity of its orbital motion, 

 it is much more impressively brought before us, when a fixed 

 mark enables us to trace its steady advance minute by minute ; 

 and there is something extremely grand and beautiful in the 

 smooth, swift motion of that ponderous globe, so perfectly 

 balanced in free space, and urged, so uninterruptedly onward by 

 the Creator's power. Occultations, especially of telescopic 

 stars, are constantly taking place, but the majority of them are 

 invisible or inconvenient from the hour, or inconspicuous from 

 the star's minuteness or the moon's brightness. The beginner 

 may be reminded that in these cases, if he lives far N. or S. 

 from Greenwich, the specified times, even though corrected as 

 they require to be for difference of longitude, will not be found 

 accurate ; for owing to the moon's comparative nearness to us, 

 each county in England refers her at the same moment to a 

 different position in the sky, and brings a different part of her 

 limb in contact with the star, occasionally raising or depressing 

 her apparent path sufficiently to let the star, occulted at Green- 

 wich, escape entirely free. The country observer, therefore, 

 especially in situations far N., must expect discrepancies, ami 

 look out in time, as the event may anticipate the tables. Ex- 

 tinction and reappearance are usually instantaneous. I once 

 (May 19, 1858) witnessed the great star Regulus snuffed out 

 in a moment, and a grand Bight it was, especially as the tele- 

 scope (an achromatic exhibited by Slater, in Boston lu>ad, 

 Islington), had upwards of 14 inches of aperture. But in some 



