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of stars were selected from Safford's Catalogue of 2018 Stars. The apparent day places, however, were obtained from the Berliner Jahrbuch whenever possible; otherwise, they were computed by the usual methods, as explained in the American Ephemeris.

Fifty-nine observations upon twenty-seven pairs of stars gave a weighted mean value for the latitude of the pier of 47° 39′ 51′′.46 0.13. The results for different nights and for different pairs of stars are given in the following table:

Results for latitude, Spokane (Washington) Station, 1896.
[S. S. Gannett, observer and computer.]

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ASTRONOMIC PIERS IN COURT-HOUSE GROUNDS AT SPOKANE, WASHINGTON.

U. S. Geological Survey latitude pier in right foreground: U. S. Coast and Geodetic Survey longitude pier behind figure of man.

LONGITUDE.

The meridional portion of the line is defined as corresponding to the thirty-ninth degree of longitude west from Washington.

Section 435, Revised Statutes, provides that "The meridian of the Observatory at Washington shall be adopted and used as the American meridian for all astronomical purposes," and this has been construed as meaning the old Naval Observatory. The latest adjustment by the United States Coast and Geodetic Survey fixes the longitude of the center of the dome of the United States Naval Observatory (old site) at 5h 08m 128.153 ± 0.049, or 77° 03′ 02′′.30 ± 0.74; hence the longitude of the meridian corresponding to the boundary line between Idaho and Montana is 116° 03' 02".30.

The United States Coast and Geodetic Survey has published an adjusted network of telegraphic longitude determinations, including points distributed in various localities throughout the United States. This system includes the Naval Observatory at Washington and also a station at Helena, Montana. From Helena the Coast Survey in 1888 determined the longitude of a pier in the court-house grounds at Spokane.

The nightly programme at each station was to observe, with an astronomic transit, two sets of ten stars each for local time, each half set consisting of four stars having a mean azimuth factor nearly.equal to zero, and one circumpolar star. Two such half sets, with a reversal of the telescope in the Y's between them, give a strong time determination. The same sets of stars were observed at Helena and at Spokane, thus giving the chronometer error for each local meridian. Between the two time sets the chronometers were compared by telegraph, thus giving the difference in time, and consequently in longitude, between the meridians within a small fraction of a second. As will be noticed in the following table, such observations and chronometer comparisons were made on four nights, when the observers interchanged places and made similar observations and chronometer comparison on four other nights, thus eliminating the effect of "personal equation."

The figures relating to this description, which were kindly furnished by the Superintendent of the United States Coast and Geodetic Survey, are presented below:

Resulting difference of longitude between the astronomic stations at Spokane, Washington, and Helena, Montana, as determined by the United States Coast and Geodetic Survey in September, 1888.

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R. A. Marr.

C.H. Sinclair.

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21 34.193 21 34.171 0.022 21 34.182 +0.208 21 34.390 6 +0.047

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Sept. 26....
Sept. 27..

Sept. 28.
Sept. 29..

Transmission time, 08.020 ± 0.002.

Personal equation, Marr-Sinclair, 0s.208 ± 0.009.

At Spokane, transit No. 19 was mounted in the grounds of the county court-house.

At Helena, transit No. 18 was mounted over the station in the northwest corner of the grounds of the United States assay office. The station was established in 1888. The court-house tower is Os.324 or 4".86 east and 0.811 south of the transit.

AASpokane-Helena 21m 34s.437+08.009.

A Helena (transit 1888), 7h 28m 088.789 ± 0.052.
A Spokane (transit), 7h 49m 438.226 08.053.

117° 25' 48".39 ± 0.80.

From the foregoing it will be observed that the probable error of the longitude determination of the Spokane pier is 0.80, or about 54 feet. Through a connection with the pier at Spokane the longitude of the meridian of the boundary line was established by triangulation and traverse, as will appear hereafter.

It may be remarked, in connection with the foregoing, that while the meridian of the Observatory at Washington is, by law approved September 28, 1850, the American meridian for all astronomical purposes, the geodetic operations of the country generally are conducted with reference to the meridian of Greenwich as an initial point. Government maps are usually referred to Greenwich, and standard time is reckoned from it.

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