yune 4, 1874] 



NA TURE 



They employ a lens of 40 ft. focus, as already described. 

 They will measure both angles of position and distances 

 from the centre, and the probable cnor of any measurement 

 will be less than i-ioo per cent. They have encountered 

 some trouble in the manufacture of their siderostats. 

 Besides photography eye-observations of contact will also 

 be made. A very able report has been drawn up from the 

 computations of I\Ir. Hill, who deserves great credit for 

 the manner in which he has completed it. This report 

 has reference to the choice of stations ; and is accompanied 

 by very valuable charts. Other reports have been made 

 upon the application of photography. 



The expeditions are to be composed of five persons 

 each. The stations of observation and the heads of 

 parties are as follows : — Wladivostock, Siberia, Prof A. 

 Hall, U.S.N. ; Nagasaki, Japan, Mr. G. Davidson, U.S. 

 Coast Survey ; Peking, China, Prof James C. Watson ; 

 Crozet's Island, South Indian Ocean, Capt. Raymond, 

 U.SA. ; Kerguelen's Island, South Indian Ocean, Lieut. - 

 Commander George P. Ryan, U.S.N. ; Hobart Town, 

 Tasmania, Prof W. N. Harkness, U.S.N. ; New Zealand, 

 Prof C. H. Peters ; and Chatham Island, South Pacific, 

 Mr. Edwin Smith, U.S. Coast Survey. 



The whole organisation has been entrusted to a com- 

 mission, the secretary of which is Prof Newcomb, who 

 has done so much valuable work for astronomy ; he has 

 taken great pains to insure success for the expedition, and 

 has visited Europe to discuss the preparations necessary 

 and to examine the instruments to be employed. 



VII. — The Italians have arranged to send out three 

 expeditions furnished with spectroscopes for the observa- 

 tion of external contact. Little is known about these 

 expeditions. 



VIII. — The Dutch are sending one expedition to the 

 island of Bourbon or Reunion. It will be furnished with 

 a photo-heliograph, which Dr. Kaiser will manipulate ; 

 Dr. Oudemans will also make observations with a helio- 

 meter. 



Having now completed our description of the details, 

 and having also given an account, so far as possible, 

 of the preparations of the various nations for the observa- 

 tions, wc shall cast a general view over the whole subject, 

 and recapitulate some of the principal details. 



The coming transit of Venus will be observed from 

 about 75 stations, at many of whicli there will be a large 

 number of instruments. The expense of the whole of the 

 expeditions will amount to between 150,000/. and 200,000/. 

 It may seem to some that the results to be arrived at are 

 not worth so great an outla)', but the general voice of the 

 non-scientific as well as of the scientific world has contra- 

 dicted this. Wherever knowledge can be gained it is worth 

 being gained ; and when individuals are unable to bear 

 the cost, it is fitting that the expenses should be incurred 

 by those governments that are really the gainers froin 

 many scientific researches for which the investigator him- 

 self frequently receives no reward. But apart from this, 

 these expeditions will lead to most valuable results. The 

 sun's distance being known, the Lunar Theory maybe vastly 

 improved, and it will be possible to determine longitudes 

 with much greater accuracy than at present. .Still more 

 will the tables of Venus be capable of re-adjustment. 

 Even now wc can calculate her place with great 

 accuracy, and this is fortunate, since it enables us 

 to predict the exact time at which Venus will 

 first come in contact with the sun, viz. 1874, Dec. 

 8d. i4h. 4m. The error to which this is liable, owing to 

 the tables, is not likely to exceed five minutes. Mr. W. 

 II. M. Christie, chief assistant of the Royal Observatory, 

 has determined the probable error in the calculated time 

 of contact arising from this cause.* He has employed 

 observations of A'enus taken at this node at the following 

 dates :-- 1872, June 28; 1873, Jan. 18; 1873, Sept. 14; 

 he has thence deduced the error in the tabular position 



^ Monthly Notices of tlie R. A. S. .\xxiv. 300. 



of Venus, and from this the error in the time of contact 

 m the coming transit. It appears from each of these 

 three comparisons that the tables of Venus give us the 

 time of contact too early ; according as we adopt the 

 first, second, or third of the above observations, the error 

 will be 7'4m., 5'3m., or 4-2in. 



Besides the astronomical advantages to be gained from 

 the coming transit, there are several collateral issues of 

 no small importance. In the first place, the longitudes of 

 a host of stations all over the globe will be accurately de- 

 teriinined, and it is a remark by no means unworthy of 

 notice that the simple observation of the local time of 

 coiitact will give the inhabitants of east Africa and of all 

 Asia an accurate means of determining their absolute 

 longitudes. If, moreover, as has been proposed, San 

 Francisco and Japan are to be compared directly as to 

 longitude, the whole circuit of the globe will be completed 

 by telegraphic and accurate chronometric determinations. 



Again, with the host of vessels by which scientific men 

 will proceed to their stations, meteorological, and some- 

 times even magnctical, instruments will be provided. 

 These vessels will be traversing the different oceans of 

 the globe about the same time, and thus the meteorology 

 of the world will be much better understood. Many ob- 

 servers will be enabled to take note of interesting pheno- 

 mena, such as hurricanes, volcanoes, and earthquakes. 

 In addition, naturalists will be appointed to accompany 

 some of the expeditions ; birds and marine animals will 

 be probably very generally collected ; the Royal Society 

 has given funds to aid in this matter. The Rev. A. E. 

 Eaton, who has made valuable collections at Spitz- 

 bergen, will examine the marine life of Kerguelen's 

 Island. Rodriguez is particularly interesting from a 

 naturalist's point of view ; it is one of the few islands in 

 mid-ocean which have not been raised by volcanic agency. 

 The remains of some extinct birds have been found there. 

 The Royal Society has appointed a geologist, a botanist, and 

 a naturalist to go to this island. There is little doubt that 

 Science in general will gain greatly by these expeditions. 



As to the main observation we can have no doubt from 

 the large number of expeditions, and from the multiplicity 

 of methods to be employed, that we shall obtain excellent 

 results, although the actual reduction of the observations 

 will be exceedingly laborious. Each nation, while it 

 generally adopts some special method for its choice of 

 stations, will also utilise other methods. Wc have seen that 

 the English, while they rely chiefly on De I'lsle's method, 

 will employ all the others except the heliometric, while 

 the Germans depend mainly upon the heliometric method. 

 The French and Americans have chosen their stations 

 with reference to photography. The Russians are to 

 compare observations of all kinds with difl'ercnt nations. 

 These countries have all co-opcratcd in the most har- 

 monious manner, partly by correspondence, and partly by 

 the personal visits of astronomers to different nations. 



Although the observations are to be made at the end of 

 the present year, the actual reduction of the observations 

 will take so long that we cannot hope for the complete 

 and final results as to our distance from the sun before 

 the year 1876. At each of the British stations the ob- 

 servers will remain at least three months to determine 

 their longitudes. 



Here we may leave the subject. The preparations are 

 for the most part completed ; many of the observers of 

 different nations are on their way to their various posts. 

 It says a great deal for the civilisation of the world that 

 on December 8 of the present year those quarters of 

 the globe will be thickly studded with emissaries from so 

 many nations to observe an important astronomical phe- 

 nomenofi. 



It will be well to conclude this series of articles with a 

 statement of the arrangements which have been made as 

 to observers on the British expeditions. It is extracted 

 from instructions published under authority : — 



