

ASTRONOMY. 401 



of the work is for hydrograpliic purposes; but it is almost equally 

 valuable astronomically. It is interesting to note that Captain Green's 

 longitude of Vladivostok is 8 h 47 m 30 8 .92, while the direct (overland) 

 longitude is 8 h 47 m 31 B .32. The small discrepancy of 8 .4 is a testimony 

 to the accuracy of the work. 



Telegraphic longitudes in South America. — The following is an extract 

 of a letter from Dr. Copeland, dated- Lima, January, 1883: "At Cho- 

 rillos, near this, are staying M. Barnaud, lieutenant de vaisseau, and 

 M. Favreau, ensigne de vaisseau, members of the French Venus Ex- 

 pedition to Chili. Chorillos is the landing point of the cable from 

 Valparaiso and Panama. The French astronomers, in conjunction with 

 two colleagues now at Valparaiso, are determining the difference of 

 longitude; they have 2-inch transit instruments, with chronographs 

 and chronometers, and the cable is led directly into the observatory. 

 The instruments are similar at both stations ; the observers do not in- 

 terchange stations, but the personal equation has been determined for 

 wire transits and signals transmitted by Thompson's galvanometer. 

 The strength of current is adjusted by a rheostat to a constant strength. 

 A triangulation will connect Chorillos, Callao, and Lima, distant some 

 6 or 7 miles from each other. The connection of Valparaiso with Buenos 

 Ayres on the one hand, and with Callao and Panama on the other, will 

 complete the circuit of the greater part of South America, the chain 

 from Greenwich to Buenos Ayres, through Lisbon, Madeira, St. Vincent, 

 Pernambuco, Bahia, Rio Janeiro, and Montevideo, haviDg been fin- 

 ished by Lieutenant Commander Green, U. S. N., in 1879. It is deeply 

 to be regretted that a spirit of undue economy prevents the British 

 Government from taking part in these important operations, which are 

 so closely connected witli navigation and geography on a large scale." — 

 (Copernicus, November 28, 1883.) 



Ghronometric longitudes. — The Gomptes Rendus for January 8, 1883, 

 contains an interesting note by M. de Magnac upon the accuracy of lon- 

 gitudes determined by chronometers. A comparison is made with the 

 values determined in 1871-1873 of the longitudes of Bahia, Montevideo, 

 and Bio de Janeiro with the telegraphic values more recently obtained 

 by officers of the United States Navy. The differences are as follows : 



Chronometric — Telegraphic. 



Bahia, — 1 8 .3. 



Bahia, +1 8 .0 



Montevideo, — 8 .5 

 Rio de Janeiro, — 1 8 .1 



This surprising accuracy, for expeditions of over forty days, is due 

 to the methqd adopted, that of M. Villarceau, in which the rate ob- 

 served on the land before departure and after the return are made the 

 basis of a calculation giving the rate from day to day as a function of 

 the time and temperature. 

 H. Mis. 69 20 



