ASTRONOMY WITH AN OPERA-GLASS. 69 



the light of Mira, it is believed that the more rapid changes of Algol 

 may be due to another cause ; namely, the existence of a huge, dark 

 body revolving swiftly around it at close quarters in an orbit whose 

 plane is directed edgewise toward the earth, so that at regular inter- 

 vals this dark body causes a partial eclipse of Algol. Notwithstand- 

 ing the attacks that have been made upon this theory, it seems to hold 

 its ground, and it will probably continue to find favor as a working 

 hypothesis until some fresh light is cast upon the problem. It hardly 

 needs to be said that the dark body in question, if it exists, must be 

 of enormous size, bearing no such insignificant proportion to the size 

 of Algol as the eai'th does to the sun, but being rather the rival in 

 bulk of its shining brother — a blind companion, an extinguished sun. 



There was certainly great fitness in the selection of the little group 

 of stars of which this mysterious Algol forms the most conspicuous 

 member, to represent the awful head of the Gorgon carried by the 

 victorious Perseus for the confusion of his enemies. In a darker age 

 than ours the winking of this demon star must have seemed a prodigy 

 of sinister import. 



Turn now to the bright star Algenib, or Alpha Persei. You will 

 find with the glass an exceedingly attractive spectacle there. In my 

 note-book I find this entry, made while sweeping over Perseus for 

 materials for this article : " The field about Alpha is one of the finest 

 in the sky for an opera-glass. Stars conspicuously ranged in curving 

 lines and streams. A host follows Alpha from the east and south," 

 The picture above will give the reader some notion of the exceeding 

 beauty of this field of stars, and of the singular manner in which they 

 are grouped, as it were, behind their leader. A field-glass increases 

 the beauty of the scene. 



The reader will find a starry cluster marked on Map 4 as the 

 "Great Cluster." This object can be easily detected by the naked 

 eye, resembling a wisp of luminous cloud. It marks the hand in which 

 Perseus clasps his diamond sword, and, with a telescope of medium 

 power, it is one of the most marvelously beautiful objects in the sky 

 — a double swarm of stars, bright enough to be clearly distinguished 

 from one another, and yet so numerous as to dazzle the eye with their 

 lively beams. An opera-glass does not possess sufficient power to " re- 

 solve " this cluster, but it gives a startling suggestion of its half-hidden 

 magnificence, and the observer will be likely to turn to it again and 

 again with increasing admiration. Sweep from this to Alpha Persei 

 and beyond to get an idea of the procession of suns in the Milky-Way. 

 The nebulous-looking cluster marked 34 M appears with an opera-glass 

 like a faint comet. 



Next look at Cassiopeia, which is distinctly marked out by the zig- 

 zag row of stars so well described by Aratus. Here the Milky- Way 

 is so rich that the observer hardly needs any guidance ; he is sure to 

 stumble upon interesting sights for himself. The five brightest stars 

 VOL. xxxii. — 5 



