THE COMING TRANSIT OF VENUS. 217 



lege Observatory and Greenwich some years ago, and it is now known 

 that the result obtained was greatly in error. Indeed, Prof. Peirce, 

 in his discussion of the series of observations, came to the conclusion 

 that it was impossible to derive the longitude of a place by this means, 

 certainly, within one second of time. 



The Americans and Russians intend to depend on the occultations 

 of small stars by the moon. 



Occultations are much more likely to be free from systematic 

 errors than the moon-culminations, and, if they can be observed 

 throughout a lunation, a compensation of errors will obtain. 



The Russians intend to mask their stations of observation, and 

 subsequently to connect by telegraph St. Petersburg with the most 

 important of them. The transportation of chronometers to and fro 

 between the stations whose longitude is thus determined and the 

 minor ones will assure the longitude of the latter. 



The American parties in the southern seas will be transported to 

 their various stations in a ship-of-war which will touch at the different 

 islands and leave the parties, and which will make chronometric 

 expeditions between the various stations. Besides this, all existing 

 telegraph-lines will be utilized. As each of the parties of each nation 

 is to be led by some astronomer of eminence, it is certain that no 

 means will be neglected to make the preliminary results of the greatest 

 attainable accuracy. 



The various assistants are now in training at Greenwich, Poltava, 

 and Washington, with the very instruments which they will use on 

 the expeditions. 



At Washington and Poltava an apparatus for the representation 

 of the transit is in use. A disk representing Venus is caused to travel 

 over an illuminated space which is representative of the sun, and the 

 circumstances of the transit are then observed. 



In this way it is hoped to obtain an idea of the personal error of 

 each observer in watching contacts, so that, in reducing the observa- 

 tions of the transit, all personality may be eliminated. 



Most of the American parties will start in the spring of 1874, and 

 proceed in the most expeditious way to their stations. They must 

 take with them every thing which they can need during their stay, 

 for in most of the stations there is no supply of any kind to draw 

 upon. 



We can hardly realize the absolute necessity of being provided 

 with every thing that may be needed on such an expedition : but let 

 us conceive the feelings of an astronomer on a desert island with no 

 screw-driver, or with no ink, or matches, or soap ! 



There is no repairing a blunder of outfitting in these cases, and the 

 greatest care has to be exercised in providing for all contingencies. 



Arrived at its station the party will put up its observatory, a little 

 wooden or canvas hut which has been brought from America, for no 



