ASTRONOMY. 203 



the same as that found by Encke. Dr. Oppolzer goes further and 

 shows that, granting the existence of such a resisting force, its effect 

 upon the motion of Faye's comet would be so small as to be confounded 

 with uncertainties of the computed perturbations. The question of the 

 existence of a resisting medium will be definitively settled by computa- 

 tions now in progress upon the other comets of short period. 



THE PLANETS. 



Vidca7i (?). — A new attemi)t to find an orbit in accordance with the 

 more or less doubtful observations of dark round spots passing across 

 the Sun's disk was published in the A. iST. by Heer v. Oppolzer. He 

 found a system of elements which was in remarkably good accordance 

 with the eight observations on which the calculations were founded. 

 Watson's observation during the eclipse in 1878 was not among these, 

 and the resulting orbit made " Vulcan" at that moment be 7° preceding 

 the Sun. A nearly central transit ought to have taken place on March 

 18, 1879, but nothing was seen, though many telescopes were directed 

 to the Sun that day. 



In Xo. 2253-54 of the A. N. Dr. 0. H. F. Peters has published a 

 long article entitled " Some critical remarks on so-called intra-Mercurial 

 Planet Observations." In the first part of this article the writer con- 

 siders at length the observations made during the eclipse of July 29, 

 1878, by Watson and Swift, of two unknown objects southwest of 

 the Sun. The fact that the line between the two stars, called a and 

 b by Prof. Watson, is almost parallel and equal in length to the line 

 between and ? Cancri, joined to the small size of the improvised circles 

 of the instrument, appears to him to prove beyond doubt that the 

 objects seen were nothing but the stars and C Cancri. The constant 

 error of about 3"", which, under this supposition, would afiect the E. 

 A.s of a and b, he explains by the different circumstances under which 

 the circle markings were made for the stars and for the Sun ; in the 

 former case, in semi-darkness and in a hurry ; in the latter case, in full 

 daylight and with leisure. Possibly, also, the markings were made at 

 the same side of the wire-pointer, thus creating a parallax of ^^ or ^^ of 

 an inch. Mr. Swift's observation is treated more summarily by Prof. 

 Peters, who thinks the confusion and successive gradations in his 

 statements must deprive every reader of confidence in them. 



To this criticism Prof. Watson has given an indignant reply in Ko. 

 2263 of the same journal. He denies flatly that his wire-pointers were 

 as easily bent as supposed by Prof. Peters, and feels confident that 

 the probable error of 5', assigned by himself, is rather too large than the 

 reverse ; the 20' of Prof. Peters he considers perfectly absurd. There 

 is only one of Prof. Peters's objections which he did not answer; he did 

 not state whether he saw a and Cancri at the same time or not in this 

 paper. This seems to be the crucial point of the whole question, and 

 Prof. Watson, in his report to the l^aval Observatory, has distinctly 



