57 



2d Result — Chronometer No. 2557, h. m. s. 



tast (at 18/i. 31m.) - - 1 15 39.74 h. ?n. s. 



h 1 15 39.74 



Result adopted — Chronometer No. 2557, Oist of si- 

 dereal time for this station (at 18/?.. 58?w.) + 1 15 39.65 



3J. The Longitude. 

 Tiie above determination of the Prairie du Chien time, and the 

 Chicago time as observed on the nights of the 12th and 15th of July, 

 already given at pp. 358 and 359 of Vol. VI. (No. 60) of the Society's 

 Proceeidings, and the rates of the two chronometers between those two 

 dates, given at page 362 of the same volume, combined with the fol- 

 lowing telegraphic signals, give us the longitude of our Prairie du 

 Chien station, as follows, viz. — 



Determination of the difference of Longitude between Chicago and. 

 Prairie du Chien, Wisconsin, by electric signals for comparisons 

 of time, July 13, 1858. 



Sidereal Chronometer xNo. 2557, fast, of Prairie du Chien sidereal 

 time, (at 18//.. 47m. sidereal time,) Ih. 15m. 396-.61. 



Rate per sidereal day, + 4s.91; or per sidereal hour, + 0s.2045. 



Mean solar Chronometer No. 141, slow, of Chicago mean solar 

 time, (at 11//. 34m. mean time,) 4m. 44s. 51. 



Rate per mean solar day, — 06'.03; or per mean solar hour, — 

 Os.0013. 



1st. — Chicago signals recorded at both stations. 



1st Mean. — Electric signals sent from Chicago to Prairie du Chien, 14 03.436 

 VOL. VII, H 



