now measuring on the Continent 195 



whole, an eligible mode of procedure. A single link failing 

 in the chain of transmission, nothing is accomplished, and the 

 whole line has to be re-established for another attempt. Ex- 

 perience has fully shown, we think, the inconvenience and 

 inexpediency of attempting too extended a transmission, with- 

 out providing for the security of a part, should the whole 

 transmission fail. In 1824, the determination was attempted 

 between Strasbourg and Paris, having two intermediate stations 

 of transmission, and, by consequence, three intermediate 

 signal-stations : the signals were continued for ten successive 

 nights, ten in each night, at each post, making altogether one 

 hundred signals. And in the same year the arc between Paris 

 and Brest was attempted by an arrangement altogether similar. 

 The latter failed wholly, nothing whatsoever being accom- 

 plished ; and in the arc between Paris and Strasbourg, six 

 transmissions only succeeded, giving a result which it has 

 since been found necessary to reject. The following year, 

 1825, both arcs were again attempted, two additional stations, 

 one a signal, and the other a chronometrical station, having 

 been introduced on the line between Paris and Brest ; and a 

 fresh arrangement of the stations, but not increasing their 

 number, between Paris and Strasbourg. The number of suc- 

 cessive nights was also increased to twelve, making one hun- 

 dred and twenty signals throughout the line. Of these, thirty- 

 five succeeded, on the line between Strasbourg and Paris ; but 

 between Paris and Brest the transmission again failed altoge- 

 ther on eleven nights out of the twelve, and the result obtained 

 on the single night was not considered sufficiently satisfactory 

 to prevent the necessity of an entire repetition of the whole in 

 the summer of 1826. The details of the third and success- 

 ful attempt have not yet been published ; but we have learnt, 

 that the precaution was adopted on this occasion of virtually 

 dividing the arc into two portions, by an astronomical station 

 midway between Paris and Brest. 



The measurement of the arc, .between Paris and Brest, gave 

 rise to a similar undertaking between Paris and Greenwich, to 

 determine the long- agitated question of the difference of longitude 

 between the respective national observatories. This was accom- 

 plished in 1825, by Colonel Bonne and M. Largeteau, on the part 



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