yune 29, 1876] 



NATURE 



195 



sion — another, to establish one's own. As we have 

 already remarked, the abandonment of Hell's solution is 

 not the demonstration of a satellite ; and we have yet to 

 hear the opposite side. Some adverse points we have 

 noted as we have passed along ; and we might have 

 added the fact that at the epoch of Rodkier's second 

 observation Uranus and Venus were not far apart ; per- 

 haps " within blundering distance." But of course the 

 main strength of the denial lies in the fact that, though 

 the alleged appearance can require but little optical 

 advantages, it has been so frequently sought in vain 

 through a long series of years. During that very spring 

 of 1764, when the primary occupied an especially favour- 

 able position, it was very carefully looked for by many 

 observers — among others, the acute and experienced 

 Messier, but nowhere seen except at Copenhagen and 

 Auxerre. Cassini and Short, with interest awakened by 

 their own apparent success, could never with all their 

 diligence recover it ; and the latter, twenty-three years 

 after his own striking observation, was thought by Lalande, 

 then in London, to disbelieve the satellite's existence. Not 

 to mention Bianchini and others, the elder Herschel never 

 saw a trace of it ; nor Schroter, the close observer of Venus 

 during fifteen years ; nor Harding, nor Struve, nor Lament, 

 Smyth, De Vico, Secchi, or any other of the first ob- 

 servers armed with the first telescopes of modern times. 

 And though the subject has now ceased to attract atten- 

 tion, yet, in the unprecedented multiplication of observers 

 and instruments, it would hardly have had a chance of 

 escape. On the whole, therefore, though the evidence 

 may exclude the intrusion of an ordinary "ghost," it 

 seems irresistible against the reality of a satellite. 



What, then, was that which was seen ? for that some- 

 thing really has been seen, the character of some at least 

 of the witnesses renders a certainty. A reflection in the 

 telescope independent of the position of the eye would 

 have been always visible as a permanent defect ; and the 

 fact of its never recurring is equally adverse to the idea 

 of a satellite, and that of an instrumental deception. The 

 only alternative which remains would seem to be that of 

 atmospheric reflection, or "mirage." There would certainly 

 be some difficulty in finding a parallel among recorded 

 facts, though Brewster, if I recollect aright, speaks of 

 having once seen two images of the crescent moon ; but 

 the known instances of atmospheric illusion are so ne of 

 them so very strange and inexplicable, and yet so abun- 

 dantly attested, that we may possibly, though with little 

 confidence, seek in this direction a solution of the ancient 

 mystery. 



Before concluding these remarks, I may be permitted 

 to relate something which fell under my own notice many 

 years ago, and which may perhaps have some connection 

 with the present subject. The observation which I am 

 about to describe took place in the year ] 823 ; it was not 

 reduced to writing till nine years afterwards, but the 

 recollection of it was then very vivid and fully to be 

 trusted ; and a small diagram of the relative position of 

 the objects made at the time in the margin of a pocket- 

 book of that year fixes the date to May 22. Until that 

 evening I had never seen the planet Mercury, but finding 

 that he was then in a favourable position I looked out for 

 him with a little common hand-telescope (my near sighted- 

 ness and the want of an eye-glass preventing me from 

 detecting him otherwise), and soon found him low in the 

 sunset horizon. The telescope in question had a good 

 achromatic object-glass ol v^ inch aperture and i4iQches 

 focus, and was fitted with a terrestrial eye-piece, magnify- 

 ing perhaps thirteen or fourteen times \ it was a favourite 

 instrument in those early days, and I had succeeded in 

 detecting with it several ot the brighter nebulae and 

 clusters, especially, at the extreme limit of visibility, the 

 large nebula in Triangulum (M. 33). When I had looked 

 at Mercury, I turned to Venus, then high in the S.W., 

 and saw a star, exactly resembling Mercury, or a minia- 



ture Venus, p or s p the planet, at fa short distance, 

 perhaps 20' or 30', and \ or ^ oi its diameter, or rather 

 its impression on the eye, as of course with so low a 

 power the disc of the planet could not be well made out. 

 I had, when 1 wrote, a very distinct recollection of its 

 great resemblance to Mercury, My mother, who had an 

 excellent sight, coming into the garden, I showed her 

 Mercury and this appearance with the glass, and she not 

 only saw it readily, but we both believed afterwards that 

 she perceived it without that aid. On the next evening, 

 or more probably on the next but one, I could not find it 

 again. As far as I can ascertain, I had in those early 

 days no knowledge of the suspicion that had been enter- 

 tained of a satellite : and I did not enter it, as in that 

 case I should have done, in a little note-book of remarks 

 able phenomena that I kept. Through the kindness of 

 Mr. Lynn I have been enabled to ascertain that the star 

 ( Geminorum was not far from the planet on that day, 

 only about 30j' further S., which would agree very fairly 

 in that direction, but lying 6^ m. more to the E. Inde- 

 pendently of this discrepancy — a serious one, for I have 

 no doubt of the/ or sp position of the satellite, not onfy 

 clearly remembered but shown in the little diagram — it 

 does not seem probable that a star of 3-4. mag. should 

 have been so conspicuous in such an instrument in the 

 twilight. I have no note of the hour, but as Mercury had 

 not sunk into the smoke of the town (Gloucester) in the 

 W. horizon, it must have been comparatively early, and 

 at that time of year the twilight is strong. It may be 

 too hazardous under all the circumstances to include this 

 with the other observations of the pseudo-satellite, but 

 there seems no reason why it should pass into entire 

 oblivion. T. W. We&b 



THE MISSING LINK BETWEEN THE VER- 

 TEBRATES AND INVERTEBRATES^ 



THE views which Dr. Dohrn has recently put forth 

 as to the details of the steps by which the verte- 

 brate stock arose out of an ancestry not very much unlike 

 the existing Annelids, are of such interest that, notwith- 

 standing previous reference to the subject, no apology is 

 needed for presenting the readers of Nature v/ith a con- 

 densation of the main argument contained in " The Origin 

 of Vertebrata." 



Dr. Dohrn first draws attention to the correspondences 

 between vertebrate and insect embryos, which have been 

 too little regarded in consequence of our designating the 

 nervous side in the one as dorsal, in the other as ventral. 

 Yet the facts that, in both, the nervous system is developed 

 on the convex side of the embryo and acquires a strong 

 convex flexure anteriorly, and that the body-cavity is 

 finally closed up on the side of the body opposite to the 

 nervous system, point to a common origin at a compara- 

 tively high level. The surface of the animal which is 

 called ventral is determined by the presence of the mouth 

 on that surface ; and if any Vertebrates had a mouth- 

 opening between the brain and the spinal cord on the 

 dorsal surface, that dorsal surface would necessarily 

 become ventral. Since, moreover, the ancestirs of the 

 Vertebrata must have had a nervous ring surrounding 

 their gullet, it would appear more reasonable to suppose 

 that the mouth-opening had been changed in the course 

 of development than that the situation of the nervous 

 centres had been altered. We are thus led to look for 

 traces of an old mouth-opening on that surface of the 

 early Vertebrates which corresponded to our dorsal sur- 

 face, and to seek reasons for regarding our present mouth 

 as a comparatively modern development. 



Dr. Dohrn believes that the old mouth passed through 

 the nervous centres between the crura cerebelli, or more 



• Der Uf'prung der Wirbelthlere und das Princip des Fiinctionwechscls : 

 Genealogische Skutzen von Anton Dohrn. (Leipzig : Eiigcluiann). 



