SECT. XXXVI. DOUBLE STARS. 395 



a spot that appeared on the 25th of May following would have 

 allowed the globe of the earth to drop through it, leaving a thou- 

 sand miles clear of contact all around this tremendous abyss. 



All the variable stars on record of which the places are distinctly 

 indicated have occurred without, exception in, or close upon, the 

 borders of the Milky Way, and that only within the following 

 semicircle, the preceding having offered no example of the kind. 



Many stars have actually disappeared from the heavens. 

 42 Virginis seems to be of the number, having been missed 

 by Sir John Herschel on the 9th of May, 1828, and not again 

 found, though he frequently had occasion to observe that part of 

 the sky. Mr. Cooper, of the Markree Observatory, has given a list 

 of fifty stars that are missing since the publication of his list of 

 stars in 1847. Comparing the present state of the heavens with 

 more ancient catalogues, a much greater number have disappeared. 



Thousands of stars that seem to be only brilliant points of 

 light, when carefully examined are found to be in reality systems 

 of two or more suns, many of which are known to revolve about 

 one another. These binary and multiple systems are very 

 remote, requiring powerful telescopes to show the stars sepa- 

 rately. They are divided into eight classes, according to the 

 proximity of the two stars. The first class comprises only such 

 as are less than 1" of space apart ; those of the second class are 

 more apart than 1" and less than 2", &c. &c. Sometimes the 

 two stars are of equal magnitude, but more frequently a con- 

 spicuous star is accompanied by a smaller companion. In some 

 cases the conspicuous star itself is double, as in Cancri, Scorpio, 

 11 Monocerotis, and 12 Lyncis, which are triple stars. Each of 

 the two stars of e Lyrse is a beautiful and close double star ; so 

 that which in a common telescope appears merely to be a double 

 star, is found to be quadruple with a very excellent instrument. 

 The multiple system of 6 Orionis is one of the most remarkable 

 objects in our hemisphere. To the naked eye and with an ordi- 

 nary telescope it seems to be a single star, but it really consists of 

 four brilliant stars forming a trapezium, and accompanied by two 

 excessively minute and very close companions, to perceive both 

 of which is the severest test of a telescope. 



The first catalogue of double stars in which thefr places and 

 relative positions are given was accomplished by the talent and 

 industry of Sir William Herschel, who made so many great disr 



