NUMBER, DISTANCE, AND MAGNITUDE OF STARS. 163 



then he may form some idea of the awful gulf between us and the stars, from the 



fact, that the triangle formed by lines 



(_____- ~"/^^~^\ drawn from the extremes of the orbit to 

 / \ a star at the vertex, has defied the most 



I ) perfect instruments of human invention to 



V J measure, so inappreciable is it. Supposing 



~^^y the whole of that orbit filled with a globe 

 resplendent as the sun, it would have a cir- 

 cumference of 600 millioHS of miles, and yet have only the appearance of a twinkling 

 atom as seen from the nearest of the stars. 



Previous to the determinations of Newton, the discovery of an annual parallax of the 

 stars was a point of great interest in order to confirm the Copernican doctrine of the 

 earth's motion in space. Though not so important on that ground now, it is an object 

 which modern astronomers have pursued with great zeal, though not with success until 

 our own time. Dr. Brinkley, the Bishop of Cloyne, conceived that he had succeeded in 

 the case of a Lyrae, the star Vega of the first magnitude in that constellation ; but improved 

 instruments have lessened the amount of parallax he assigned, and Mr. Airy has pro- 

 nounced it too small to be sensible. The grand problem of stellar remoteness has 

 however been solved by Professor Bessel, and has been justly called a magnificent 

 conquest. 



Bessel commenced this great achievement in the month of September 1834, at 

 Konigsberg, and was employed upon it during the four following years, communicating 

 the result in a letter to Sir John Herschel in 1838. "After so many unsuccessful 

 attempts to determine the annual parallax of a fixed star," he remarks, " I thought it 

 worth while to try what might be accomplished by means of the accuracy which my 

 great Fraunhofer heliometer gives to the observations. 1 undertook to make this in- 

 vestigation upon the star 61 Cygni, which by reason of its great proper motion, is perhaps 

 the best of all, which affords the advantage of being a double star, and on that account 

 may be observed with greater accuracy, and which is so near the pole, that, with the 

 exception of a small part of the year, it can always be observed at night at a sufficient 

 distance from the horizon." This star, now one of the most interesting in the heavens, 

 is in the right wing of the Swan, about 7J S. by E. of Dened, a second class star in 

 that constellation. It is of the fifth magnitude, and in our latitude passes the meridian 

 near the zenith. As intimated in the preceding extract, 61 Cygni has long been known 

 by a motion of its own in space, so extraordinary, independent of that which its constitu- 

 ents may have about each other, that Arago supposes its velocity to exceed that of 

 Mercury, the most rapid body of the solar system, sixty thousand times. In watching this 

 star, Bessel commonly took observations sixteen times every night. Without detailing 

 the course he pursued, which would be uninteresting and unintelligible to most readers, 

 it will be sufficient to state, that our Astronomical Society testified its confidence in his 

 researches and their result, by awarding to him its gold medal. His determination of 

 the annual parallax of the star is 0'* 3136, or somewhat less than one third of a second, 

 which places it from us at the astonishing distance of 657,700 times the radius of the 

 earth's orbit, or nearly 62J billions of miles. To aid the imagination in forming some 

 idea of this interval, it may be stated, that the conflagration of the star would not be 

 announced to us under a period of ten years, for a ray of light, which darts to us from 

 the sun in eight minutes, would require that time to travel through the space between us 

 and it. As to that standing example of velocity in terrene regions, a cannon ball, with 

 its rush of five hundred miles an hour, it must be allowed to travel some fourteen millions 

 of years to compass such a space. One delicate thread of a spider's web, placed before the 



