76 THE WANDERINGS OF THE NORTH POLE. 



The effect thus produced was that of a number of circular arcs of 

 varying- sizes and of different degrees of briglitness. Most conspicu- 

 ous amongst tliem was the tiail x^roduced by the actual j)olar star 

 itself. It is well known, of course, that though the situation of the 

 pole is conveniently marked by the fortunate circumstance that a 

 bright star happened during the luesent century to lie in the immedi- 

 ate vicinity of the veritable pole, yet, of course, this star is not actually 

 at the pole, and consequently, like all the other stars, Polaris itself 

 must be revolving in a circle whereof the center lies at the true pole. 

 The brighter the star the brighter is the trail which it produces, so 

 that the circle made by Polaris is nuich more conspicuous than the 

 circles produced by the other stars of inferior luster. It is however 

 to be noted that some of the faint stars lie much closer to the pole than 

 Polaris itself. There is indeed one very minute object so close to the 

 pole that the circle in which its movements are performed seems very 

 little more than a point when represented on the screen on which the 

 slide was projected. The interesting circumstance was noted that there 

 appeared to be occasional interruptions to the continuity of the circular 

 arcs. This was due to the fact that clouds had interposed during the 

 nitervals represented by the interruptions. A practical application is 

 thus suggested, which has been made to render useful service at Har- 

 vard College Observatory. Every night, and all night long, a plate is 

 there exposed to this j)articular part of the sky, and the degree in 

 which the Pole-star leaves a more or less complete trail affords an indi- 

 cation of the clearness or cloudiness of the sky throughout the course 

 of the night. From the positions of the parts where the trail has been 

 inrerru})ted it is possible not only to learn the amount of cloudiness 

 that has prevailed, but the particular hours during which it has lasted. 

 This interesting system of concentric j)olar circles affords us j^erhaps 

 the most striking visual rej)resentation that could possibly be obtained 

 of the existence of that point in the heavens which we know as the 

 pole. The picture thus exhibited was a striking illustration of the 

 Copernican doctrine that the diurnal stellar movement was indeed only 

 apparent, being of course due to the rotation of the earth on its axis. 



Suppose that a photograph, like that I have been describing, were to 

 be taken at intervals of a century, it would be found that the center 

 of the system of circles, that is to say, the veritable pole itself, was 

 gradually changing on the heavens. I do not by this mean that the 

 stars themselves would be found to have shifted their i)laces relatively 

 to each other. No doubt there is some effect of this kind, but it is an 

 insignificant one, and need not at present concern us. The essential 

 point to be noticed is, that the stars which happen to lie in the vicinity 

 of the pole would have a changed relation to the pole in consequence 

 of the fact that this latter point is itself in incessant movement. At 

 the present time the pole is advancing in such a direction that it is 

 getting nearer to the Pole-star, so that the actual circle which the Pole- 



