NA TURE 



597 



THURSDAY, OCTOBER 23, 1879 



THE INTRA-MERCURIAL PLANET QUESTION 



IN No. 2253-54 of the Astronomische Nachrichien, Dr. 

 C. H. F. Peters, the discoverer of so many minor 

 planets, has " Some critical remarks on so-called intra- 

 Mercurial planet observations,"includingthe observations 

 reported by Prof. Watson during the totality of the 

 eclipse of July 29, 1878. Replies to these remarks have 

 since appeared from Prof. Watson and also from Mr. 

 Lewis Swift, of Rochester, New York, who, it will be 

 remembered, also considered he had seen an object which 

 could be no known star or planet. Prof. Peters enters 

 upon other cases where intra-Mercurial bodies have been 

 suspected, but we shall confine ourselves mainly here to 

 his criticism of Prof. Watson's observations during the 

 last eclipse. His object is to adduce evidence disproving 

 Watson's conclusion that he had seen one, probably two 

 unknown planets, and he grounds his argument chiefly 

 upon the small size of the circles to which Watson trusted, 

 and the fact that nearly on the parallel of his two objects 

 a and b, and at an almost equal distance, a small one, in 

 right ascension, were the stars 6 and f Cancri. He 

 states that the circles of wood with paper scales pasted on 

 them, were only 5 and \\ inches respectively in diameter, 

 and as Prof. Watson estimated the probable error of a 

 position given by them at only five minutes, the space 

 would measure on the circles only t,\^ of an inch, and 

 further he states that the wires which served as pointers 

 "were so elastic as easily to give way several degrees 

 under the touch by a pencil." So far, therefore, from 

 accepting Watson's estimate of the precision of his 

 readings. Prof. Peters thinks he does him no injustice in 

 supposing that they were made " at the utmost to ^ inch, 

 corresponding to twenty minutes of arc upon his circles ; " 

 and in this case, the differences of a from 6 Cancri, and 

 of b from f Cancri, or + 2m. 55s. and -|- 3m. 23s. 

 respectively, he believes may be explained by the errors 

 in the markings or readings. It is also urged that the 

 markings for the sun were made under circumstances less 

 hurried than those for the suspected planets. Watson 

 estimated the objects at the time of 4 and 4J magni- 

 tude, and, remarking that absolute magnitude must be 

 quite uncertain under such conditions, Peters points out 

 that the difference of brightness corresponds pretty nearly 

 with that given by Argelander, Hcis, and others between 

 f and 6 Cancri; and he adds, "it is, therefore, quite 

 apparent to every unbiassed mind that Watson observed 

 fland f Cancri, nothing else." It should be added that Prof. 

 Peters attempts to explain the ruddiness of the object near 

 6, — "If the sand ledge, tmder the lee of which the telescope 

 was standing had nothing to do with it ; " the observation, 

 perhaps, teaches that the corona possesses the property 

 of less absorbing the red rays, and may, therefore, be of 

 some value. It seems also, in his view, that the corona 

 gives a disk to the stars, or calms down the radiations to 

 a kind of spurious disk, as a slight fog does; and as he 

 does not admit that the power employed would show a 

 real disk, we are to assume this was the case during Prof. 

 Watson's observations. With regard to Mr. Swift's 

 observations, it is represented that his successive publi- 

 VoL. XX.— No. 521 



cations offer so singular a gradation ^in the statements as 

 to unfit them to be the subject of a scientific discussion. 



As we have stated, Prof. Watson has replied to the 

 criticisms which the Clinton astronomer has published to 

 " make evident beyond cavil how erroneous the conclu- 

 sion too rashly rushed at by the observers." He protests 

 against mis-statement of the facts connected with his 

 observations, remarking that it appears to him "the 

 grossest of unfairness to attempt to discredit an observa- 

 tion made by an experienced observer by deliberately 

 misrepresenting the circumstances of the observations," 

 So far from the pointers of his circles bending under 

 the touch by a pencil, they were made of unannealed 

 brass wire one-eighth of an inch in thickness, not 

 filed to a point, but to a knife-edge, placed vertical to 

 the plane of the circle ; they were quite rigid, and could 

 not be disturbed in the least by the pencil when 

 marking. The probable errors attributed to his read- 

 ings Watson declares to be absurd, and says that any 

 one interested may, by a few trials ascertain that by 

 the method he adopted it is possible to measure without a 

 greater probable error than 2' ; the limit of 5' which he 

 gave was an outside one. Peters had urged that a 

 practised observer would have compared the object a 

 directly with B Cancri, as the two would have been in the 

 field together with the telescope employed, to which Prof. 

 Watson replies, and with justice, that besides the want of 

 time for such direct comparison, the method he was 

 applying was different. If he had known that a new star 

 would present itself near 6 Cancri, he could have prepared 

 himself for direct comparison ; under the circumstances 

 his plan of securing rapid indication of the position of 

 any object that might be visible seems to have been as 

 effective a one as could have been devised, and, as Dr. 

 Draper termed it when it was explained to him the night 

 before the eclipse, "a good dodge." Further, Watson 

 observes that the assertion that his circles " were of wood, 

 with paper scales pasted on to them, and wires serving as 

 pointers," shows conclusively that Peters either did not 

 yet understand his method, or that he was " purposely 

 mis-stating the circumstances of his observations." 



Finally, he makes what he terms these emphatic declara- 

 tions : — " I. I observed, during the total eclipse of July 29, 

 1878, a new star between 6 Cancri and the sun, and south 

 of the sun, whose position and magnitude were as already 

 published by me. 2. I observed another star, which I 

 believe to be a new star, whose magnitude and position 

 were as already published by me." Whether or not these 

 objects were intra-Mercurial planets he does not positively 

 assert, but he had the right to express the hones belief 

 that they were. Watson adds that he " hopes ere long 

 to give good reason for the faith that is in him," by 

 which we understand him to imply that he has the inten- 

 tion to enter further upon the subject. 



We will venture to say that the general feeling amongst 

 astronomers when first reading Prof. Watson's announce- 

 ment of his observations during the totality of the eclipse 

 of 1878, of one, if not two, unknown objects, would be 

 that a man of such known ability and experience as an 

 observer, and so good a practical astronomer, as shown, 

 amongst other proofs, by his able treatise on practical 

 astronomy, would not risk his whole scientific reputation 

 by putting forth such a statement to the world, unless he 



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