79 



h. m. s. 



Brought forward, +0 11 45.69 



Longitude of Chlcaffo station No. 3, - - +5 50 31.20 



Determination Isf. 

 Longitude of the centre of Washington Square in the 

 City of Rock Island, west of tlie meridian of 

 Greenwich, - - - - - 6 02 16.89 



P. S. Since presenting the above result, I made, on the 29th of 

 July, 1859, another visit to the City of Rock Island. It was made 

 the occasion of a second determination of the longitude of that place, 

 depending on the time-observations at Chicago given under the dates 

 of July 28th and 31st, the time-observations at the City of Rock 

 Island of July 29th, as given below, and the electric signals of that 

 night. The observations at the same Rock Island Station which was 

 before occupied, were as follows, viz. — 



1st, Observations for the Time. I8r>9, July '29th. At the centre 

 of Washington Square. 



Sidereal chronometer No. 2557, fast: h. m. s. 



By 3 observations on e Bootis, west (at \Sh. 08m.) + 1 57 25.19 

 By 4 observations on fCygni, east (at 18A. 18m. 405.) + 1 57 25.63 



Result — Chronometer No 2557, fast of sidereal time 



for this station (at 18/^. 13m. 20.s.) - + 1 57 25.41 



The night was cloudy, but the sky opened clear just long enough 

 to enable us to make the few observations above recorded. They 

 were worked separately and the results were satisfactory. The 

 extreme difference, for chronometer error, in the three on $ Bootis, 

 west, being Os.33 and in the four on f Cygni, east, being 15.03. The 

 extreme difference in three (the first not being counted) on fCygni, 

 is O5.47. They were all, however, taken into the count. 



These stars being nearly of the same declination, north, (e Bootis 

 27° 40' and f Cygni 29= 39'), the result for the time at Rock Island, 

 this night, may, we think, be considered satisfactory. 



The elapsed time between the Chicago observations which apply 

 to the first determination (that of March 1st), was five days. That 

 between the Chicago observations which enter Into the calculation 

 of this second determination, is only three days. Considering all 

 circumstances we are inclined to assign equal weight to the two de- 

 terminations. The second one is as follows, viz : — 



