374 Work for the Telescope. 



able pairs to a future opportunity ; many other beautiful objects 

 are succeeding them, but the nights are so short that the tele- 

 scope is not likely to be much in requisition: and we shall 

 therefore postpone for the present the description of such as 

 may be equally well seen later in the year, and confine ourselves 

 to a small number, which, from their nearness to the horizon, 

 are passing speedily away, or cannot be observed, during 

 ordinary hours, at any other than the present season. 



8. 7 Virginis. 1-6. 77°-9. (1831-38). round, (1836-06). 

 l"-9. 191'-6. (1843-33). 3"-8. 169°-9. (1858-39). Both 4. 

 Silvery-white and pale yellow, the latter the less brilliant. 

 Struve pronounced them alternately variable ; this seems con- 

 firmed by some observations of Smyth, Dawes, and Fletcher ; 

 and, as Humboldt remarks, probably indicates a very slow 

 rotation of both suns upon their axes. In every respect a most 

 remarkable pair. No stars are more unquestionably binary, 

 and none have run so interesting a course, combining such 

 varied distances and velocities. Cassini II. perceived that this 

 was a double star at Paris in 1720, with a distance of about 7"' 5, 

 fully half that of Mizar. Since that time the components have 

 been approaching with a gradually accelerated speed, and after 

 a most rapid perihelion, or rather periastron, passage in 1836, 

 have been widening out again, and are now a comparatively 

 easy object, at least 4" apart. At the nearest appulse, Sir J. 

 Herscheks great reflector at the Cape failed to exhibit any 

 other than a circular disc; and the splendid achromatic at 

 Poulkowa, near St. Petersburg', with an object-glass of about 

 14| inches in diameter, and a power of 1000, was only able 

 just to indicate, what was proved by the undiminished light to 

 the naked eye, that there was no actual eclipse. The orbit 

 has given a great deal of trouble to computers, from the inac- 

 curacy of some of the observations. Admiral Smyth has 

 laboured most diligently in clearing up the difficulties which 

 beset his favoxirite object; and on the whole Sir J. Hcrschcl 

 considers that the period must lie between 140 and 190 years : 

 about 180 seems the more probable duration. 



There is little difficulty in finding 7, from a, Spica Virginis, 

 the principal star in the constellation. Spica is on the meridian 

 about 8k. 30m. in the early part of June, and is the most con- 

 spicuous star in the southern sky : 7 is tke nearest bright star 

 to tke right of it, and a little above it. 7, as well as ij Virginis 

 a little W. of it, and £ further off to the E., arc all near enough 

 to the equator to measure the diameter of tke field ofview. 



9. 8 Corel. Algorab. 23"-5. 210*-9. 3 and 8i Pale 

 yellow and purple. Sestini calls the small star white. This 

 pleasing pair is easily found, being .that nearest to Spica of the 

 four principal stars in Corvus, and forming an equilateral 



