Longitude of Chicago observing station No. 3, west

of the meridian of Greenwich,

Longitude of the Toledo observing station, west of

the meridian of Greenwich,

Equal, in are, to

Latitude, as before,

0 16 21.63

+5 50 31.20

+5 34 09.57 83° 32′ 23.55 W. 41° 39' 02".26 N.

From true azimuths from observations on Polaris, with the theodolite, and measured distances from the observing station, we are enabled to give the following table of the latitudes and longitudes of positions in the city of Toledo, viz.—

On the map accompanying the report of Captain Andrew Talcott, of his operations and observations in determining the boundary line between the States of Michigan and Ohio, in the year 1833 (see Doc. No. 497 of the House of Representatives, of the 23d Congress, 1st Session), he places Toledo in latitude 41° 38′ 43′′, and in longitude 83° 22′ 28′′=5h. 33m. 29.87s. west of Greenwich, as near as we can measure by the map scale. Our latitudes agree well, considering the difference of stations occupied ; but in longitude, my determination places Toledo 9' 50" in arc 39.33s. of time west of the position given to it on Captain Talcott's map, as printed on a scale of 5 miles to 1 inch, to accompany his report. This difference in longitude is equal to 8.48 statute miles.

Station.

X. PRAIRIE DU CHIEN, WISCONSIN.

This station is 122 feet due north from the front door of the Telegraph Office at the depot of the Milwaukee and Mississippi Rail Road, on the left bank of the Mississippi river.

1st. Observations for the Latitude. 1858, July 13th. By 10 observed altitudes of a Ursa Minoris (Polaris,) north, combined with 24 circum-meridian altitudes of B Aquarii, south; Latitude of station

O

43 02 01.35 N.

The sky was so much clouded to the north, all night, that I could obtain no more than ten observations on Polaris, and ẞ Aquarii was the only star that could be observed on, south, for the latitude. It was only by watching the sky until an hour and a half past midnight, that the above result could be obtained. Still later watching was necessary, as will presently appear, to obtain the desired observations for the time at this place.

2d. Observations for the Time. Same night. Sidereal chronometer No. 2557, fast:

Mean from 2 West Stars (at 19h. 52m.) 1 15 40.04

By 12 observations on Cygni, east

(at 17h. 10m.)

1 15 39.43

Result adopted-Chronometer No. 2557, fast of si

dereal time for this station (at 18h. 58m.)

3d. The Longitude.

1 15 39.74

+1 15 39.65

The 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 Proceedings, and the rates of the two chronometers between those two dates, given at page 362 of the same volume, combined with the following 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 No. 2557, fast, of Prairie du Chien sidereal time, (at 18h. 47m. sidereal time,) 1h. 15m. 39s.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 11h. 34m. mean time,) 4m. 44s.51.

Rate per mean solar day, Os.03; or per mean solar hour,

0s.0013.

1st.-Chicago signals recorded at both stations.

1st Mean. Electric signals sent from Chicago to Prairie du Chien, 0 14 03.436

VOL. VII.-H

2d.—Prairie du Chien signals recorded at both stations.

2d Mean.-Electric signals sent from Prairie du Chien to Chicago, 0 14 03.422 1st Mean.—Electric signals sent from Chicago to Prairie du Chien,

as above,

- 0 14 03.486

Result:-Prairie du Chien observing station is west, in longitude, of Chicago observing station No. 2, by a mean of the two sets of signals,

Longitude of Chicago observing station No. 2, west of the meridian of Greenwich,

Longitude of Praire du Chien observing station, west

of the meridian of Greenwich,

Equal, in arc, to .

Latitude of this station, as above,

+0 14 03.429

S.

h. m. +5 50 31.15

6 04 34.58 91° 08′ 38.7 W. 43° 02' 01.35 N.

The above determination will be found, we think, to correspond very nearly with that of Mr. J. N. Nicollet, derived by him from observations made in the year 1839, while employed in exploring the hydrographical basin of the Mississippi. His station was the American Fur Company's house, near Fort Crawford. An interesting discussion of the several observations which led him to the longitude which he adopted for that station, will be found in his report at page 117, of Senate Document No. 273, of the 26th Congress, 2d Session, printed in the year 1843.

He there states the longitude of that point to be, West of the meridian of Greenwich,

Equal, in arc, to

h. m.

S.

6 04 35.55

91° 08' 53".25*

In his table of geographical positions, however, at page 123, he states that position to be in

Latitude

Longitude, west from Greenwich,

43° 03' 06" N.

6h. 04m. 37.3s.

*Erroneously printed in that document, 93°, &c.

I only spent the night in observing at Prairie du Chien, and was obliged to leave that place early the next morning, on my return to Chicago. Hence I had no opportunity for making any survey to connect our two stations, and thus determine accurately their relative positions. In looking up the Mississippi, however, from my station, I observed that its course upward appeared, when compared with the direction of the North Star (Polaris) to be a very little west of north. The difference of our longitudes, reduced to a common point, is not probably more than one second of time; and, judging by the eye, of the distance from my station to the Fur Company's old house, our latitudes appear to agree very closely.

XI. DUNLEITH, ILLINOIS.

Station. One hundred feet east from the left shore of the Mississippi river, between the freight depot and the passenger house of the Northwestern terminus of the Illinois Central Rail Road. From the observing station to a point perpendicularly under the most northern of the two cupolas on the north end of the ticket office, of this rail road depot, is S. 13° W. 250 feet, horizontal measurement.

1st. The Latitude. 1859, February 22d. By 37 circum-meridian altitudes of ẞ Orionis, south, combined with 24 altitudes of Polaris (« Ursæ Minoris,) north,

Same night.-By 26 circum-meridian altitudes of a Hydræ, south, combined with 14 other altitudes of Polaris, observed 5 hours later than the previous set,

Result-Latitude of station,

42 29 45.16

42 29 44.65

42 29 44.9 N.

2d. Observations for the Time. 1859, February 21st. Sidereal chronometer No. 2557, fast:

1st Set. Before the telegraphic signals.