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Island county, Illinois-published in 1857, on a scale of 1 mile to 1 inch- to our Station XVII., we obtain the approximate positions of several places in the vicinity, as follows, viz.

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XVIII. FORT ARMSTRONG, ILLINOIS.

This old fort is situated on the point at the west or lowest extremity of Rock Island; an island in the Mississippi river, between the "City of Rock Island" and the City of Davenport.

By Hogane & Lambach's map of the City of Davenport, published in 1857, on a scale of 9 inches to 1 mile, or 5863 feet to the inch; and on C. H. Stoddard's map of the cities of Rock Island, in Illinois, and Davenport in Iowa, published in 1851, on a scale of 13.2 inches to 1 mile, or 400 feet to the inch,-scales which admit of minute measurements of courses and distances,--Fort Armstrong is laid down in reference to the centre of Washington Square, in the City of Rock Island, our astronomical station, XVII., as follows, respectively, viz.—

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In Captain Andrew Talcott's report on the Ohio and Michigan boundary, made in January, 1834, he gives the position of Fort Armstrong to be in latitude 41° 31′ 09".7 N., and longitude 90° 27′ 15′′* = in time to 6h. 01m. 49s., exceeding us in the latitude, say 10', and falling short of us in the longitude 26s.55 in time = 6m. 38s.25 in arc = 5.736 miles.

On Nicollet's map, the lower extremity of Rock Island (occupied by Fort Armstrong), is laid down 1' 20" in latitude less, and 8′ of longitude, == 6.91 miles more than our observations indicate. On the last War Department map (of 1857), it is laid down in latitude 35" of latitude south, and 5' 24" in longitude west of the position given by our observations.

XIX. DAVENPORT, 10WA.

This beautiful city occupies the height and slope of an eminence, on the right bank of the Mississippi river, immediately opposite to the City of Rock Island, Illinois.

A mean, derived from courses and distances measured on Stoddard's map of 1851, and Hogane & Lambach's map of 1857, mentioned before, and referred to our astronomical station XVII., gives us as follows, in regard to Davenport, Iowa, viz.—

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On Nicollet's map, Davenport is placed 18" in latitude south, and 7' 37" in longitude west of our position, derived from the preceding observations.

On the War Department map of 1857, it is placed 16 seconds of latitude south, and 6 minutes and 5 seconds of longitude west of the position which our observations assign to it.

* Erroneously printed 90° 26' 15 in his report, as contained in Doc. No. 497, of the House of Representatives, 23d Congress, 1st Session. See page 6 of that document.

XX. NEW BUFFALO, MICHIGAN.

This place is situated on the south east shore of lake Michigan, nearly opposite to Chicago.

Station. In Mr. Joshua R. C. Brown's garden. From this station to the point of intersection of the axes of Whitaker Avenue and Mechanics Street, is S. 5° 12′ W. (true) 106 feet.

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By 35 circum-meridian altitudes of a Virginis, south, combined with 32 altitudes of Polaris (a Ursæ Minoris) north; latitude of station,

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Reduction to the intersection of the axes of Whitaker
Avenue and Mechanics Street,

Latitude of the point of intersection of Whitaker
Avenue and Mechanics Street,

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2d. Observations for the Time. 1st. 1859, March 16th. Sidereal chronometer No. 2557, By 3 observations on a Tauri, west (at h. m.

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fast:

By 8 observations on Capella (ɑ Auriga), also west (at 9h. 04m.)

By 11 observations on 2 West Stars,

giving weight according to the
number of observations on each,
(at 8h. 53m.)

S.

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1 25 07.46

1 25 07.37

1 25 07.42

+1 25 07.42*

By 10 observations on a Bootis, east (at 9h. 44m.) +1 25 09.18*

Result-Chronometer No. 2557, fast of sidereal time

for this station (at 9h. 19m.)

+1 25 08.30

Clouds prevented the selection of the best time-stars; and none were visible for the latitude.

Here it is evident that too great an index error for the sextant was used in computing the altitudes for the time by the East and West stars. That error had changed since last observed, which is the cause of the difference of results East and West;-the west observations giving too little, by an unknown quantity, and the east observations giving too much by the same quantity. The mean of the two results eliminates the error, and gives J. D. G. the correct time as reported.

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This result for the New Buffalo time, and the results of the timeobservations at Chicago on the nights of the 15th and 19th of March, —which last was the earliest date after our return to Chicago from New Buffalo, that observations could be made, owing to bad weather— combined with the following telegraphic signals, give us our 1st determination of the longitude of New Buffalo, viz.—

Determination of the difference of Longitude between Chicago and New Buffalo, Michigan, by electric signals for comparisons of time, March 16th 1859.

Sidereal Chronometer No. 2557, fast, of New Buffalo sidereal time (at 10h. 34m. 28s. sidereal time), 1h. 25m. 08s.66.

Rate per sidereal day, + 6s.793; or per sidereal hour, + Os.283. Mean solar Chronometer No. 141, slow, of Chicago, mean solar time (at 10h. 54m. mean time), 4m. 40s.25.

Rate per mean solar day,

0s.0039.

08.094; or per mean solar hour,

1st.-Chicago signals recorded at both stations.

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1st Mean. Electric signals sent from Chicago to New Buffalo,

2d.-New Buffalo signals recorded at both stations.

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2d Mean. Electric signals sent from New Buffalo to Chicago, Electric signals sent from Chicago to New Buffalo,

1st Mean.
as above,

Result:-New Buffalo Observing Station is east, in longitude, of Chicago observing station No. 3, by a mean of the two sets of signals,

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Longitude of Chicago Station No. 3,

1st Determination.

h. m. S.

+5 50 31.20

Longitude of New Buffalo Station, west of the meridian of Greenwich,

5 46 59.68

On the 19th of May, I found I should be obliged to visit New Buffalo harbour again, so I determined to make it the occasion of another trial of the difference of longitude between that place and Chicago. For this purpose the observations, as recorded, were made at Chicago on the night of the 19th; and also on the night of the 21st, on my return from New Buffalo. The night of the 20th was spent at New Buffalo, where the following time-observations were made at the same station as before, viz.—

1859, May 20th.-Sidereal chronometer No. 2557, fast of New Buffalo sidereal time:

By 3 observations on a Coronæ Bo

realis, east (at 12h. 51m.)

S.

h. m.

1 33 13.59

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By 5 observations on y' Leonis, west, (at 13h. 40m.) +1 33 12.52

Result-Chronometer No. 2557, fast of New Buf

falo sidereal time (at 13h. 29m.)

+1 33 12.91

The night was not favourable for observation. The sky was much clouded, which again prevented a selection of the best time-stars. Those that were observed on were caught, at favourable moments, be

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