OBSERVATIONS FOB LONGITUDE. 23 
LONGITUDE. 
The meridional portion of the line is defined as corresponding to 
te thirty-ninth degree of Longitude west from Washington. 
Section 435, Revised Statutes, provides thai "The meridian of the 
bservatory at Washington shall be adopted and used as the Ameri- 
m meridian for all astronomical purposes," and this has been con- 
pued as meaning the old Naval Observatory. The laiesi adjust ment 
y the United States Coast and Geodetic Survey fixes the longil ude of 
le center of the dome of the United States Naval Observatory (old 
te) at 5 h 08 m L2M53± B .049, or 77° 03' 02". 30 =L 0". 74; hence the 
►ngitudeof the meridian corresponding to the boundary line between 
laho ami .Montana is 11G° 03' 02". 30. 
The United states Coast and Geodetic Survey has published an 
djusted network of telegraphic longitude determinations, including 
oints distributed in various localities throughout the United States. 
'his system includes the Naval Observatory at Washington and also 
station at Helena, Montana. From Helena the Coast Survey in 
888 determined the longitude of a pier in the court-house grounds 
t Spokane. 
The nightly programme at each station was to observe, with an 
stronomic transit, two sets of ten stars each for local time, each hall 
et consisting of four stars having a mean azimuth factor Dearly equal 
i> zero, and one circumpolar star. Two such half sets, with a reversal 
>f the telescope in the Y's between them, give a strong time deter- 
uination. 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 
elegraph, thus giving the difference in time, and consequently in 
ongit ude, between the meridians within a small fraction of a second. 
Vs will be aoticed in the following table, such observations and chro- 
lometer comparisons were made on four nights, when the observers 
nterchanged places and made similar observations and chronometer 
comparison on tour other nights, thus eliminating the effecl of •' per- 
sonal equation." 
