260 



KNOWLEDGE. 



[No\'EMBEB 1, 1897. 



with phases similar to those of Venus, the earth would 

 offer a whitish cloudy appearance, with occasional 

 clear spots, or patches darker than the rest, which 

 might reappear at the same hour of the day ; and it 

 would turn under its envelope, which would be frequently 

 opaque, without any of its geographical configurations 

 showing their periodical displacements of twenty-three 

 hours fifty-six minutes. Sometimes, no doubt, our atmo- 

 sphere is partly transparent, and might allow some details 

 near the centre to be seen. But that of Venus is too dense 

 ever to display so satisfactory a state of transparency. 



It is chiefly — nay, solely — upon the elongated grey spot, 

 visible between the terminator and the limb of the planet, 

 that M. SchiapareUi rests his theory. He believes that 

 this spot is real and permanent. We see, in fact, pretty 

 frequently a grey shading of this kind, and this year in 

 particular we have observed it with the equatorial of the 

 Juvisy Observatory. But it is seen equally on the eastern 

 and western crescents— that is to say, in different and 

 opposite regions. This year, for example, I have shown 

 the eastern half of Venus, in my drawing of July llth 

 (Venus being a morning star), whereon this grey trace is 

 marked, as it also is in M. Anto- 

 niadi's drawing of August 30th. 

 In the views taken by M. Schia- 

 pareUi, however, the western half 

 is shown (Venus being an evening 

 star). Hence, besides the difficul- 

 ties already mentioned, it would 

 have to be assumed that the 

 planet was symmetrical on either 

 side of the variable terminator 

 meridian — that it has the shape, 

 say, of a melon, with the poles of 

 the longitudinal ribs or segments 

 precisely coinciding with the cusps 

 of the crescent. That would in- 

 deed be a novel theory to estab- 

 lish. It appears that the spot 

 upon which the two hundred 

 and twenty-four days' rotation is 

 founded is more nearly related to 

 the terminator and to the ter- 

 restrial observer than to the sun ; 

 it is relatively to the earth that 

 it appears fixed, and not relatively to the sun. 



(8.) I am now coming to the latest observations, for, 

 indeed, this article is already of an extravagant length in 

 spite of my endeavour to be as concise as possible. I will 

 only therefore mention, by the way, the labours of Messrs. 

 Vogel, Terby, Trouvelot, Perrotin, Denning, Niesten, 

 Stuyvaert, Barnard, Stanley Williams, MacEwen, Brenner, 

 and others. We can compare their observations, and the 

 same divergence will be found between their various 

 drawings ; nothing is certain, nothing settled, nothing 

 permanent ! Light shadows ; optical effects produced by 

 contrast with the terminator ; atmospheric phenomena 

 due to solar heat, clouds, vapours, etc. 



Mr. Lowell writes in his turn as follows, in reference to 

 the observations of 1896 : '■ — " The configurations have 

 always been very sharply defined — as sharply, indeed, as 

 those of the moon ; they are, moreover, liru's rather than 

 spots. Several radiate from certain points. And not only 

 are these lines permanent, but they are also constantly 

 visible ; nothing prevents their being seen, except the 

 clouds of our own atmosphere. The period of rotation 



* Bulletin de la SociHJ Aslronomique tie France, 1897, pp. 139 

 and 2.53. 



Fig. 7. — A View of Venus 

 taken by M. SchiapareUi, 

 July 31st, 1895. 



coincides with the period of revolution. This platwt is a 

 desert." And here (Fig. 8) are two of Mr. Lowell's illus- 

 trations : — 



X~J7' 



Oct' /5, t'^J?" 



FlO. 8. — The Planet Venus as drawn by Mr. Lowell in 1896. 



This description and these drawings, so entirely at 

 variance with all that has gone before, " put the final seal 

 of certainty," as M. SchiaparelU expresses it, to our 

 opinion, viz., that nothing certain can be descried upon 

 the surface of Venus, and that whatever has hitherto been 

 written regarding its period of rotation must be con- 

 sidered null and void. 



In all probability the globe of Venus revolves, invisible 

 to us, under its atmosphere, which turns with it, but 

 which affords us no reference points fixed and capable of 

 allowing us to determine this rotation. 



There may possibly be a chance of ascertaining it by 

 means of the spectroscope, applied to the opposed east and 

 west limbs, at those epochs when the phase is not too 

 conspicuously marked. Most likely the northern and 

 southern extremities of the disc are not far from the poles, 

 and the edges of the disc are simply atmospheric outlines. 



This atmosphere is so dense that its action upon the 

 deformation of the globe is apparent, even during the 

 transits of Venus, in the shape of a black disc across the 

 surface of the sun. M. Bouquet de la Grye, from photo- 

 graphs he took at Puebla, during the transit of December 

 8th, 1874, ascertained the existence of certain raised 

 portions, which he attributed to the condensation of 

 equatorial vapours and to polar glaciers of great height,* 

 while he estimated for the atmosphere of Venus a height 

 five times as great as that of the earth. These views 

 concerning the situation of the poles tally remarkably well 

 with my own observations and those of my coadjutors at 

 Juvisy t with reference to the polar white spots, as well 

 as with those of M. Trouvelot. Other observers have seen, 

 and drawn, these same white spots, both north and south, 

 but without regarding them as polar. There are besides 

 here indisputable optical effects ; but they do not disprove 

 the reality of these spots, as M. SchiapareUi has recognized 

 on his part, though he has denied their polar character. 



This year, indeed, we have taken a great many drawings 

 at the Juvisy Observatory, of which nine were repro- 

 duced in the plate in the October Number of Knowledge. 

 The observations were made in full daylight — generally 

 between 8 a.m. and 12 noon. They show very few details. 

 The least doubtful dark spots proved to be the grey marks 

 near the horns ; also a vertical diffused streak at three- 

 eighths of the distance between the terminator and Umb. 

 The extreme shades are shown in aU the sketches, while 

 that near the centre appears in Figs. 2, 4, 5, 6, and 7. In 

 addition a protuberant whiteness was glimpsed on the 11th 

 of June, near the southern horn (Fig. 1). This object, 



* Bulletin de la Society Astronomique de France, 1891, p. 96. 

 t Bulletin de la Socu'tc Astronomique de France, 1895, p. 12. 



