2d Result-Chronometer fast (at 8h. h. m. S. Result adopted-Chronometer No. 2557, fast of sidereal time for this station (at 7h. 31m.) +1 38 38.42 +1 38 38.27 Having so good a determination of the time by this night's observations, it was a great disappointment, when we went to the telegraph office, to find the communication with Chicago cut off at La Salle, through some misunderstanding there. We were thereby prevented from passing any electric signals this night, but were obliged to wait until the next night. 1859, March 1st. Same Station. Sidereal chronometer No. 2557, fast: By 8 observations on a Leonis, east (at 6h. 34m.) By 9 observations on ' Leonis, also east (at 7h. 04m.) h. m. S. 1 38 42.18 1 38 42.22 By 13 observations on a Tauri, west (at 8h. 15m.) Result-Chronometer No. 2557, fast of sidereal time for this station, (at 7h. 32m.) +1 38 42.21 +1 38 42.20 The above observations for the time at the City of Rock Island, on the nights of February 28th, and March 1st, give the rate of chronometer No. 2557, for the 24 hours between those dates, +3s.93. This rate applied to the period of the chronometer error of the 1st of March, together with the time observations made at Chicago on the 27th of February and the 4th of March, and the following telegraphic signals, give us the longitude of our "City of Rock Island" station. Although we returned from Rock Island to Chicago on the evening of March 2d, yet the weather continued so cloudy until the night of the 4th, as to prevent our making earlier observations for the time here. Thus we have to depend upon five days run of chronometer No. 141, to obtain its rate to be applied to the observations of February 27th, in order to get the Chicago mean solar time of the signals of the 1st of March. Determination of the difference of Longitude between Chicago and the City of Rock Island, by electric signals for comparisons of time, March 1st, 1859. Sidereal Chronometer No. 2557, fast, of Rock Island, sidereal time (at 8h. 55m. 42s. sidereal time), 1h. 38m. 42s.43. Rate per sidereal day, + 3s.93; or per sidereal hour, + Os.1637. Mean solar Chronometer No. 141, slow, of Chicago, mean solar time (at 10h. 29m. 44s. mean time), 4m. 43s.50. 1st.-Chicago signals recorded at both stations. -- 2d.-Rock Island signals recorded at both stations. Difference of Longitude by each signal.Rock Island west of the meridian of Chicago observing station No. 3. h. m. s. 0 11 45.687 Times of signals given at Rock Island by sidereal Chronometer No. 2557. S. h. m. S. correct sidereal time of Rock Island signals. h. m. 8. 10 38 43.50 9 16 28.74 9 04 43.05 h. m. 8. h. m. 8. 0 11 45.69 h. m. 1st Mean. Electric signals sent from Chicago to the City of Rock Island, as above, Result:-Rock Island Station is west, in longitude, of Chicago observing Station No. 3, by a mean of the two sets of signals, +0 11 45.69 Longitude of the centre of Washington Square in the 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. 1859, July 29th. of Washington Square. Sidereal chronometer No. 2557, fast: By 3 observations on By 4 observations on Bootis, west (at 18h. 08m.) Result-Chronometer No 2557, fast of sidereal time for this station (at 18h. 13m. 20s.) 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 0s.33 and in the four on Cygui, east, being 18.03. extreme difference in three (the first not being counted) on Cygni, is 0s.47. They were all, however, taken into the count. The These stars being nearly of the same declination, north, (ɛ Bootis 27° 40′ and 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 determinations. The second one is as follows, viz :— Determination of the difference of Longitude between Chicago and the City of Rock Island, Illinois, by electric signals for comparisons of time, July 29th, 1859. Sidereal Chronometer No. 2557, fast, of Rock Island sidereal time (at 19h. 53m. 36s. sidereal time), 1h. 57m. 25s.94. Rate per sidereal day, 78.61; or per sidereal hour, +0s.317. Mean Solar Chronometer No. 141, slow, of Chicago, mean solar time (at 11h. 36m. mean time), 1h. 57m. 25s.94. Os.755; or per mean solar hour, 1st.-Chicago signals recorded at both stations. Times of Signals given at by mean solar No. 141. h. m. s. 11 31 09 11 34 00 11 36 50 1st Mean. h. m. 8. h. m. 8. Electric signals sent from Chicago to the City of Rock Island, Difference of Longitude by each signal. City of Rock Island west of the meridian of Chicago observing station No.3. h. m. 8. 0 11 46.227 2d.-The City of Rock Island signals recorded at both stations. h. m. 22 02 44 22 05 44.5 22 08 45 8. h. m. 8. 11 42 40 to Chicago, Rock Island correct sidereal time of Rock Island signals. 11 47 44.20 20 17 04.22 20 05 18.00 2d Mean.-Electric signals sent from the City of Rock Island 1st Mean. Electric signals sent from Chicago to the City of Rock Island, as above Result:-The centre of Washington Square in the City of Rock +0 11 46.228 h. m. S. Longitude of Chicago Station No. 3, Brought forward +0 11 46.23 2d Determination. July 29th, 1859. Longitude of centre of Washington Square, in the +5 50 31.20 6 02 17.43 6 02 16.89 Result, giving each Determination an equal weight: Equal, in arc, to Latitude of the same station, as before given, 6 02 17.16 90° 34' 17'.4 W. 41° 30' 37".8 N. By survey, departing from this station, based on an observed azimuth of the sun on the 2d of March, 1859, for comparing our courses with the true meridian, we obtained the positions of other points, in the City of Rock Island, which may be useful for future reference. We give them all in the following table, viz.— On the War Department map of 1857, the City of Rock Island is laid down in latitude 41° 28′ 39′′ N., and longitude 90° 39′ 13′′ W.; which is 2 minutes of latitude less, and 4′ 31′′ more, in longitude, than our observations give. Note.--By applying a transcript from the Land Office Surveys, contained in C. H. Stoddard's map of Scott county, Iowa, and Rock VOL. VII.-L |