NA TURE 



[March i8, 1875 



Not only was the angle of calculation drawn exactly, but the com- 

 puted time was drawn to the nearest minute. After first contact, the 

 measurement of cusps proceeded at intervals of five seconds. Near 

 the moment of second contact, a cloud interposed, liut it cleared 

 away almost instantly, and enabled the astronomers to obtain 

 the moment of second contact a little late, and to proceed with 

 the measurement of distances of the limb of Venus from the sun's 

 limb. This ended the part of the astronomical observers for the 

 time being. Meanwhile the photographers were hard at work. 

 During this time, half an hour, no fewer than forty-five photo- 

 graphs were taken of the sun. From this lime until the Transit 

 was over, photographs were taken whenever breaks in the mist 

 gave the opportunity, the mist growing into clouds as the day 

 wore on, gradually shutting out the sun from sight. In all, sixty- 

 five photographs were obtained, including several of the different 

 stages of egress. " 



Our readers will no doubt remember what has been said 

 about the high strategic value of Kerguelen. " For the 

 Delislean method," to quote the article in the Thiies, 

 "relied on by the English chiefly, it is the. station at 

 which (the Crozets being unoccupied) ingress was most 

 retarded. Next in value to it from this point of view 

 came St. Paul's Island (of which more presently), and 

 then Bourbon, Mauritius, and Rodrigues. 



" Further, tlie entire Transit was visible from Kerguelen, 

 therefore observations of duration could be made, and there- 

 fore it was a Halleyan station, and, let us add, the Southern 

 Halleyan station of the very highest value. Thus, com- 

 bining observations made at Nertchinsk and Kerguelen, 

 we get a difference of duration of thirty-two minutes ; the 

 more easterly group of stations lying round New Zealand 

 combined with Nertchinsk, only giving a difference of 

 some twenty-eight minutes at the outside ; and Mauritius, 

 combined with the same place, only giving twenty-four 

 minutes. For the photographic or direct method also it 

 was of the highest importance, combining the photo- 

 graphs taken with those secured in Siberia and India. 

 We are now, then, in a position to analyse the telegram. 

 Observations of ingress retarded to combine with the 

 observation of ingress accelerated, made at the Sandwich 

 Islands, have been secured by three parties. We may 

 say, then, that the Delislean observations have been suc- 

 cessful. Unfortunately, we gather that the photographic 

 record of the interior contact is wanting. This, however, 

 is of less value, as the Sandwich Island party, with an 

 ingenious confusion of the subjective and objective, have 

 already informed us that ' Janssen failed.' 



" As in no case did the same observer secure both ingress 

 and egress, the value of the observations for the appli- 

 cation of the Halleyan method is doubtful ; but the last 

 reference — ' Americans obtained some photographs ' — 

 may, when the work comes to be finally discussed, prove 

 to be the most important of all, and astronomers all over 

 the world will be very anxious to know the precise success 

 attained, and it is very probable that it was great. 



"Although we have thought well to wait for the news 

 ■ from Kerguelen before contmuing our Notes, it must not 

 be imagined that no intelligence of interest has been 

 received since the last Notes appeared. On the contrary, 

 the real interest is increasing as the details arrive ; be- 

 sides which, the French have received news from their 

 parties at St. Paul's Island and Campbell Island, stations 

 evidently outdoing even Kerguelen in the wretchedness 

 entailed upon the observing parties, though that seems 

 much to say after the report to the Admiralty which we 

 published, yesterday ;" while details ol the observations 

 at New Caledonia were given in last week's Nature 

 by one who took part in them. "jAt St. Paul's Island 

 the observations have been most satisfactory, as both in- 

 ternal contacts were observed and numerous photographs 

 were obtained. This is gocd news for the partisans of all 

 three methods, ingress being greatly retarded here, as 

 before stated. Unfortunately, the still more heroic occu- 

 pation of Campbell Island has been without result. 

 ' Venus seen before ingress only ; no contacts ; all well,' 



is the news telegraphed from San Francisco, which must 

 have cost M. Bouquet de la Grye a heavy pang to send 

 home. 



" We next come to the more detailed accounts, and 

 among these, that forwarded by M. Janssen to the Secre- 

 tary of the French Academy of Sciences demands the 

 first place. After describing all the care he took in the 

 choice of his station, he goes on : — 



"Some days before the Transit, our fears were increased. 

 Nevertheless, on the morning of the ninth the weather was 

 pretty good, although the sky was a little overcast. The first 

 contact was secured by M. Tisserand and myself. In the 8-inch 

 equatorial, of which the object-glass is very good, the image of 

 Venus appeared very round and well defined, and the relative 

 motion of the disc of the planet with regard to the solar disc 

 went on in a geometrical manner, without any appearance of 

 ligament or black drop. But rather a long time elapsed between 

 the moment at which the disc of Venus was tangent to the sun's 

 limb internally and that of the appearance of the fine line of 

 light between them. This anomaly I ascribe to the atmosphere 

 of the planet. I caused a photograph to be taken at the instant 

 the contact appeared to be geometric, and on the plate the con- 

 tact had not yet taken place. M. d'Almeida obtained a plate 

 containing forty-seven photographs of tlie solar limb which 

 leads to the same conclusions. I intend to discuss these observa- 

 tions, which seem to me to lead to important consequences. 



"After the first interior contact, M. .Picard and M. Arens 

 took as many photographs as possible, but the clouds greatly 

 hindered us. 



"Finally, near the second interior contact, the sun cleared as 

 if providentially, and M. Tisserand was able to determine the 

 time with precision. The sky was perfectly covered at the time 

 of last exterior contact. 



" During the Transit even we got news from Kobe that the first 

 two contacts had been observed, and that fifteen photographs 

 had been taken, and, finally, shortly after our own observations, 

 M. de la Croix announced that he had obtained the last two 

 contacts, the last one only uncertain. 



" He then concludes : — 



" I must not conclude without referring to an observation 

 which relates to the corona and the coronal atmosphere of the 

 sun. With glasses of a certain violet-blue colour, and very pure, 

 I was enabled to see Venus before she had touched the sun's 

 disc. She was visible as a small, very pale, round spot. When 

 she commenced to bite into the sun's disc, this spot completed 

 the black segment which was visible on the sun. It was a 

 partial eclipse of the coronal atmosphere. ... I saw Venus 

 two or three minutes of arc from the sun's limb. 



" There are two points in Dr. Janssen's report of the 

 greatest importance and interest. It seems not improbable 

 that his observation of a geometric contact with the eye 

 at the moment the contact was not complete to the photo- 

 graphic plate may be connected with Prof. Tacchini's 

 observation with the spectroscope, to which we have 

 referred in previous Notes. If the observation may be 

 depended upon — and Janssen, it is not too much to say, 

 is one of the best astronomical observers living — it is 

 clear that the sun built up by the blue rays was smaller 

 than the sun built up by the particular rays which in the 

 telescope employed produced white light. 



" The second point is the observation of Venus on the 

 coronal atmosphere by means of violet glass. This 

 attempt shows Janssen's genius in a remarkable manner. 

 It is based upon the idea, derived from the eclipse work in 

 1 87 1, that the coronal atmosphere is very rich in violet 

 light, the idea in its turn being based upon the fact that 

 the photographic corona is vastly different from the corona 

 seen through a train of prisms. Of course, if this be so, 

 the atmospheric light, which is not rich in violet rays, 

 may be cut off by a glass of a dark-blue colour, which 

 nevertheless will transmit the violet light coming from 

 the corona, and so show Venus as a black spot. 



" We condense the following details of the work done 

 at the Australian stations from the Melboimie Argus : — 



" At the Melbourne Observatory, presided over by Mr. R.L.J. 

 EUery, Government astronomer, the weather, by a happy chance, 



