194- 



NATURE 



\yu7ie 29, 1876 



20' from Venus ; it is expressly stated that the obser- 

 vation was repeated several times, and that after all he 

 was not certain if it was not a small star ; which, with a 

 power of between forty and fifty, was not surprising. 

 The next evening and on the 7th and nth it was again 

 seen, rather more distant, and each time in an altered 

 position, but with the same phase as its primary ; and on 

 the 7th it was seen, and even much more distinctly, when 

 Venus was not in the field. The improbability is obvious 

 of such persistency in an illusion so readily detected. 

 The cause may indeed have lain in the object-glass ; 

 such telescopes have been known. Wargentin, at Stock- 

 holm in the same year, found that his instrument pro- 

 duced a deception from this cause ; and the 6- inch 

 Cauchoix achromatic at Rome showed minute comites to 

 bright stars a little too frequently for the credit of those 

 who trusted it. Montaigne's changed position-angles 

 may be thought to indicate this cause of error, as his 9-ft. 

 refractor probably admitted of rotation in its bearings, 

 but it is a singular coincidence that these changes should 

 all have been m the direction of orbital revolution, and 

 still more, in such proportions as to be reconcilable with 

 Lambert's calculated period of about eleven days ; and it 

 is quite unintelligible that he should not have subsequently 

 detected the fault in his telescope, as from his estimation 

 of angles and distances he was evidently not a novice in 

 observation. Three years later, in 1764, Rodkier, in Co- 

 penhagen, saw such an appearance on two evenings with a 

 power ot thirty-eight on a 9^ ft. refractor ; on the latter 

 occasion with a second telescope also. There is little in 

 this to contravene the Vienna theory, especially as this 

 second telescope had a coloured meniscus eye-glass, and 

 he failed in finding it with two other instruments : but it 

 is more remarkable that on two evenings a week later 

 the same telescope told the same tale to four different 

 observers, one of whom was Horrebow, the Professor of 

 Astronomy, and who, we are assured, satisfied themselves 

 by several experiments before the second observation that 

 it was not a deception. That the necessary conditions 

 for its being such could have been maintained before so 

 many eyes, is, notwithstanding its admitted pale and 

 uncertain aspect, what could not possibly have been anti- 

 cipated. But we have not yet done with this temporary 

 outbreak, so to speak, of visibihty. Before this month of 

 March was ended, Montbarron at Auxerre, far removed 

 from all possibility of communication, and with a very 

 different kmd of telescope, a Gregorian reflector of thirty- 

 two inches, which of course was fixed as to its optical 

 axis, perceived on three separate evenings, at different 

 position-angles, something which, though it had no distin- 

 guishable phasis, was evidently not a star, and which he 

 never could find again. 



There remains still the observation of the celebrated 

 optician Short. It is indeed chronologically misplaced 

 here, but has been intentionally deferred as affording the 

 strongest point in the whole affirmative evidence. As his 

 own account is an interesting one, and has seldom, if ever, 

 been reprinted, our readers may not be displeased to see 

 it here as it stands in Phil. Trans, vol. xli. : — 



" An Observation on the Planet Venus (with regard to 

 her having a satellite), made by Mr. James Short, F.R.S., 

 at sunrise, October 23, 1740. — Directing a reflecting tele- 

 scope ot i6'5 inches focus (with an apparatus to follow 

 the diurnal motion) towards Venus, I perceived a small 

 star pretty nigh her ; upon which I took another telescope 

 of the same focal distance, which magnified about fifty or 

 sixty times, and which was fitted with a micrometer in 

 order to measure its distance from Venus, and found its 

 distance to be about 10° 2' o" {sic). Finding Venus very 

 distinct, and consequently the air very clear, I put on a 

 magnifying power of 240 times, and to my great surprise 

 found this star put on the same phasis with Venus. I 

 tried another magnifying power of 140 times, and even 

 then found the star under the same phasis. Its diameter 



seemed about a third, or somewhat less, of the diameter 

 of Venus ; its light was not so bright or vivid, but exceed- 

 ing sharp and well defined. A line, passing through the 

 centre of Venus and it, made an angle with the equator of 

 about eighteen or twenty degrees. I saw it for the space 

 of an hour several times that morning ; but the light of 

 the sun increasing, I lost it altogether about a quarter of 

 an hour after eight. I have looked for it every clear 

 morning since, but never had the good fortune to see it 

 again. Cassini, in his Astronomy, mentions much such 

 another observation. I likewise observed two darkish 

 spots upon the body of Venus, for the air was exceeding 

 clear and serene." 



It has been justly asked by Schorr whether this 

 observer, who was the greatest optician of his time> must 

 not have known his telescopes better than to mistake the 

 reflection of Venus on the eyeglass for a satellite ? And 

 Lambert puts the case very strongly, remarking that 

 Short had the object before him for a whole hour with 

 greatly varied powers, and it is not probable that he kept 

 his eye immovable all the time, and after every change 

 in the telescope replaced it at the precise point where the 

 apparent position and distance from Venus would con- 

 tinue unaltered, especially as he used so high a power, 

 with which the slightest change would have been remarked, 

 and a micrometer, the employment of which would have 

 necessarily implied movement in the eye. Lambert might 

 have further strengthened his argument had he had an 

 opportunity of consulting the original record, which 

 shows that another telescope was employed, making in 

 all four eye-pieces, and that Short viewed it not con- 

 tinuously, but at intervals during an hour, increasing 

 every time the chance of detection ; nor should the im- 

 portant consideration be overlooked that, with the higher 

 powers, the apparent motion of the planet through the 

 field would be rapid enough to give the illusion a move- 

 ment in the reverse direction, which would unmask it at 

 once. An examination of one of Short's reflectors might 

 be necessary to decide whether with his power of 240 (he 

 was said to have considerably over-rated his magnifiers) 

 the field would have included the attendant with the 

 primary. 



The evidence against Father Hell's explanation had 

 even previously become very formidable. The conditions 

 under which his "ghost" is visible are so restrained, the 

 limits so narrow, that there is considerable presumption 

 in any individual case against such an illusion having 

 been formed, or at least against its having passed unchal- 

 lenged, when a trifling change in the supposed obliquity 

 of indirect vision would at once shift the position of the 

 false image with respect to its origin, and an equally 

 minute alteration in the distance of the eye would deface 

 or obliterate it. But if this is so in each separate instance, 

 the enumeration of so many, with instruments and 

 observers so varied, increases the improbabihty afresh at 

 every remove, and the careful observation of a man like 

 Short is peculiarly conclusive against the possibility of 

 deception, at least from the assigned cause. 



Thus far the advocates of a satellite have it their own 

 way ; and to what has been said they would add some 

 curious facts as corroborative evidence. The object, when 

 its size has been remarked, has always been recorded of 

 the same magnitude, one-fourth, or less than one-third, of 

 its primary. It showed itself seven times in one month 

 (March 1764), at a period when telescopes were no longer 

 in their infancy, and in two places at a great distance 

 from each other. And its position-angles, which chance 

 would have placed anywhere, agree sufficiently well with 

 orbital revolution to admit of the calculation of a period, 

 which Lambert has given at i id. 5h., to which, however, 

 Schorr prefers his own of I2'i7d. Many astronomical 

 details are probably accepted among us for which there 

 are no stronger grounds of belief. 



But it is one thing to invalidate an opponent's conclu- 



