NATURE 



121 



THURSDAY, DECEMBER 17, 1874 



THE TRANSIT OF VENUS 



IT is not too early to congratulate the world of science 

 upon a grand triumph. The telegrams which have of 

 late been flowing in almost incessantly from all parts of 

 the Northern Hemisphere — now from far Japan and from 

 Siberia, recording the success of French, Russian, and 

 American parties ; and now from America, giving fuller 

 details regarding the doings of the latter— leave no doubt 

 whatever that the weather has been better at the northern 

 stations than might have been expected, seeing that the 

 observations have been made in the winter half of the 

 year. 



Nor has the Northern Hemisphere been the only one to 

 give us news. We already know of success at Melbourne 

 and Hobart Town, at which place was an American party 

 similarly equipped to those at Wladiwostok in Asiatic 

 Russia, and at Nagasaki ; and Prof. Newcombhas already 

 telegraphed to the Times that the eighty photographs 

 taken by the American method at these places, combined 

 with the 1 13 taken at Hobart Town, are sufficient to give 

 us a value of the solar parallax with a probable error of 

 perhaps one-fortieth of a second of arc. This gives a 

 foretaste of what photography is likely to do for us in this 

 and the coming Transit of 18S2. 



Before we proceed to detail the observations at the 

 various stations, it will be well to re-state the various ways 

 in which a Transit of Venus may be observed. This we 

 will do almost in the words employed in a former article. 



We have the utilisation of a Transit— 



(a) By the determination of times of contact at different 

 stations, combined with a knowledge of the longitudes of 

 those stations. 



(Ji) By the determination of the least distances between 

 the centres of the sun and Venus during the Transit, ob- 

 served from different stations. 



This last determination^may be made by — 



([) What is called Halley's method; or, if we wish that 

 the world should forget a great work accomplished by a 

 former great Astronomer Royal, we may term this the 

 " method of durations." 



(2) By the Photographic method ; or, 



(3) By the Heliometric method, i 



Premising that the first method of determination (a) 

 was devised by Delisle, we have now our nomenclature 

 sufficiently complete for present purposes, and we may 

 begin with the stations at which this method can be best 

 employed. Of these ,we have four groups : Accelerated 

 Ingress, Sandwich Islands; Retarded Ingress, Kergue- 

 len's Land, Heard or Macdonald Island, Mauritius, 

 Bourbon, and Rodriguez ; Accelerated Egress, Campbell 

 Island, Emerald Island, Auckland Island, Royal Com- 

 pany's Island, and New Zealand ; Retarded Egress 

 stations in Western Russia, Persia, and Egypt. 



Of these groups the northern ones can be used for 

 Delisle's method solely, as only Ingress or Egress is seen ; 

 Ingress in the Sandwich Island group. Egress in the 

 Western Asiatic group. But the southern groups may be 

 used for all methods. 



For the methods we have grouped under {b), stations in 

 Vol. XI. -No. 268 



Eastern and Southern Asia, combined with those in the 

 Southern seas which we have already named, and stations 

 between them, such as Melbourne and Adelaide, may be 

 employed. 



From the Sandwich Islands, Kerguelen's Land, Heard 

 Island, Mauritius, Bourbon, and Rodriguez we have of 

 course not yet heard ; we consequently know nothing of 

 Delislean observations of Ingress. 



Of observations of Accelerated Egress on this method we 

 know nothing,but with regard to Retarded Egress we know 

 that the English and Russian parties in Egypt have been 

 wonderfully successful. At Teheran, a second class 

 Russian station, but better adapted than Egypt for 

 applying the Delislean method, the observations were a 

 perfect success. At Ispahan, a German party obtained 

 nineteen good photographs ; but north of this, in the 

 most favourable point of all, the Russian parties at Ormsk, 

 Astrachan, and in all that region, there was complete 

 failure. 



From the English party several telegrams have been 

 received since our last number appeared : a long one by 

 the Times, and several shorter ones by the Astronomer 

 Royal. These we give : — 



" Cairo, Dec. 9. — The Transit of Venus was observed in 

 all its phases by the astronomers of the Government 

 Expedition in Egypt this morning, at the Central Station 

 at Mokattam Heights. It was observed by Captain Orde 

 and Mr. F. M. Newton at Suez, and by Mr. Hunter at 

 Thebes. It was photographed by Captain Abney, and 

 observed by Dr. Auwers and Prof. Dollen, also by 

 Colonel Campbell and others. During the last three days 

 the weather has been very bad, and this morning the 

 telescopes in Cairo and Suez were directed to the eastern 

 quarter of a sky clouded over, showing, however, a few 

 breaks, which gave hope. Glimpses through the clouds 

 exhibited Venus as a distinct black spot on the sun, but 

 no opportunity was given for a micrometer measurement 

 for nearly half an hour after sunrise ; then a few chances 

 were given through the openings in the clouds. A decided 

 opening occurred of a very hopeful character about ten 

 minutes before contact, and after one more cloud, which 

 passed over two or three minutes only before the critical 

 epoch, the observation of internal contact was made 

 satisfactorily at every station in Egypt, and the photo- 

 heliograph has done its work well. The sky was quite 

 clear for the measurement of cusps and any observations 

 that could be made of external contact. The astrono- 

 mers are satisfied with their observations. The phases 

 are declared in Cairo to have so closely resembled those 

 shown by Sir George Airy's model at Greenwich that it 

 was hard to divest the mind of the idea that it was only 

 model practice again. The Khedive has taken a warm 

 interest in the work, and guarded the Mokattam station 

 from intrusion by cavalry pickets. By means of the tele- 

 graph line he put up to Mokattam Heights, interchanges 

 of telegraph time signals have been made between that 

 station and Greenwich, Suez, and Thebes. This expedi- 

 tion has now, therefore, nearly completed its work, and 

 in a few days will probably break up." 



Capt. Ord Brown, R.A. (Mokattam), Dec. 9 : — 

 "The egress of Venus was observed at Mokattam this 

 morning. There has been much bad weather and anxiety. 

 All well now. Contact seen through very slight haze 

 with [the] Lee [Equatorial] at about i3h. 25m. 25s. side- 

 real, and with De la Rue I3h. 22m. 21s. (Observe in the 

 Greenwich book of observation with the model ; my 

 egress is always after other observers, except Mr. Gill's.) 

 Clouds spoilt much double image work, but many limbs 



