NUMBER, DISTANCE, AND MAGNITUDE OF STARS. 161 



least with a small glass which I had in my pocket." "Surely," he adds in another 

 passage, " the situation alone is enough to inspire philosophy." 



To measure the distance of the stars, is a task which has baffled the ablest men, armed 

 with the best instruments for the purpose, and using them with the utmost nicety and 

 perseverance. Until our own day, the conclusion arrived at had only been negative. It could 

 merely be demonstrated, that the nearest of these bodies must at the least be removed from 

 us a certain space, the extent of which requires the billions of our arithmetic to express. It 

 is clearly ascertainable, that the enormous interval intervening between us and that remote 

 wanderer in our system, Neptune, is but a narrow chasm compared with the interval 

 between him and the most contiguous of the stellar orbs. On observing the same star, 

 lying in the plane of the earth's orbit, from the two extremities of the orbit, at the end of 

 six months, no perceptible alteration in the apparent size of the star can be discerned, 

 notwithstanding this vast change of situation. The inference therefore is, that the 

 diameter of the earth's orbit, the immense line of 190 millions of miles, bears no sensible 

 proportion to the real distance of the stars. But another method adopted to measure the 

 great gulf, and most laboriously pursued for more than two centuries, has been the 

 detection, if possible, of an annual parallax of the stars, or apparent change of place 

 caused by being viewed from opposite extremities of the earth's orbit. All the planets, 

 even the remotest, appear in veiy different places when viewed at the vernal and 

 autumnal equinoxes, or at any two extreme points of our globe's path; and if the angle 

 subtended be given, the distance may be calculated. But no parallax of a star amounting 

 even to a single second has been detected, and Bradley makes the observation, which Sir 

 John Herschel confirms, that if such an amount of parallax existed, it could not possibly 

 have escaped notice. Supposing, however, a parallax of one second perceptible, that, 

 by the rules of trigonometry, would give a distance from us of more than 19 billions of 

 miles; but as there is no such quantity detectable, there is no star lying within that 

 range they all lie beyond it ! 



Parallax is the apparent change of place which an object undergoes through an 

 observer shifting his own position. The traveller in journeying marks a great change in 

 the same scenery, in the disposition of its various features, by the alteration of his own 

 point of view. He observes the trees, fields, and hedgerows, which appeared in a direct 

 line between him and some distant hill, at one station, making an angle with the eminence 

 as seen from another station. Suppose we stand at a, and have two trees before us in 



the direct line a b c, both will be 

 projected to the same point d, but 

 if we shift our position to e, then 

 the nearest tree will be seen in the 

 direction /, and the farthest in the 

 direction g. By measuring the base 

 line a e, and the angles a b e, and 

 a c e, or the parallax, the niathema- 

 * tician readily arrives at the distance 

 of the trees from the points of observation. Now, with reference to estimating the 

 distances of the stars, we have the diameter of the earth's orbit as a capital base 

 line to work upon, a real change of place occurring annually on our part in relation 

 to them amounting to 190 millions of miles. Yet, notwithstanding this vast alteration 

 of position, no angle of the value of a second has been found with certainty in the 

 case of any star. 



The diagram now subjoined, exhibits the earth at two extreme points of its orbit. 

 Let the reader keep in mind the 190 millions of miles between those points, and 



