THE INTRA-MERCURIAL PLANETS. 719 



The two stars appeared red to him, shining at three degrees south- 

 west of the sun, and presenting large disks of the fifth magnitude. He 

 adds that he saw no other star, not even Delta, and that the distance 

 between them was from 7' to 8' of arc. (" Nature," September 19, 1878.) 



The two stars seen by Swift, then, are not the same two seen by 

 Watson. The matter is a good deal confused. 



Further, in observing the star Zeta Cancri, two stars could have 

 been seen, instead of one, for Zeta is a double star. It is, indeed, a 

 triple star, but a high power is required to see it triple, whereas a 

 moderate power easily shows it double. But, inasmuch as only very low 

 powers were employed, it is probable that no new cause of perplexity 

 exists here. 



To sum up : While it is possible that the American observers saw 

 an intra-Mercurial planet, or even two, we can not, in view of the 

 special difficulties of the situation, the confusion of the figures, and the 

 negative observations of the other observers, concede it to be an abso- 

 lute and incontestable fact that they saw even so much as one. The fact 

 is not yet certain. 



We would remark that no variable star is known to exist at that 

 part of the heaven. Might it not be a comet ? It did not present the 

 characteristics of a comet. 



Whatever the upshot may be, this discussion goes to show that in 

 astronomy nothing is accepted without being first verified, and that this 

 science is becoming more and more worthy of its reputation of being 

 the exactest and the most absolute form of human knowledge. 



This strange vicinage of the sun is unfortunate indeed in the annals 

 of astronomy. Time and again have observers supposed that they 

 saw planets passing before the sun ; and, out of all the observations 

 which have been made, there is not one which definitively settles the 

 question. 



The penultimate astronomical observation announced as appertaining 

 to an intra-Mercurial planet was that of the German astronomer Weber, 

 which was presented to Leverrier by Wolf, of Zurich, as having been 

 made April 4, 1876, at Peckeloh. " A small, well-rounded disk of 13' of 

 arc appeared suddenly during a partial clearness of the sky (eclaircie), 

 which was turned to account for observing the sun. It was impossible 

 to pursue the observation, owing to clouds.'* Wolf calculated that this 

 observation accorded with two prior observations made in 1859 and in 

 1820, and fixed the period of the planet at forty-two days. Leverrier, 

 too, seemed disposed to accept this observation, which gave occasion for 

 a new memoir by the illustrious French astronomer, in which he brought 

 together and compared all the observations of this kind. The stir 

 which this made in the scientific periodicals is still remembered. But 

 yet the little black disk observed by Weber was not a planet at all, but 

 merely a sun-spot, round and without penumbra. It had been observed 

 five hours earlier at the Observatory of Madrid and at the Observatory 



