The Laws Observatory. 503 
The mean 
: 38° 56 51”.70 + 0”.08 
is adopted as the 
mean latitude of the center of the pier of the 2-inch transit 
instrument in the transit room of this Observatory. 
The close agreement of these two determinations of the 
mean latitude must, of course, be taken as largely accidental, 
since it is so much closer than can be expected in the nature 
of the case, 
I have however effectually guarded myself against any pos- 
sible bias of judgment in reducing and discussing the observa- 
tions, by keeping myself in total ignorance of the corrections 
for latitude variation until the reductions were finished. The 
final results, as given above, of both determinations of the 
latitude were deduced and adopted before I had any knowl- 
edge whatever concerning the reductions to mean latitude, 
which were computed afterward. 
Til. THE LONGITUDE. 
The longitude of this Observatory was determined by 
exchange of telegraphic signals with the Observatory of 
Washington University, St. Louis, on October 25, 26, 28, 29 
and November 2, 1891. Good observations for clock cor- 
rection were secured on all these nights both in Columbia 
and in St. Louis. The signals exchanged on the first three 
nights were automatic, on the last two nights they were 
arbitrary. 7 : 
The Observations at Columbia were made by myself with 
the 2,1,-inch transit instrument of this Observatory, mounted 
in its usual place on the west pier in the transit-room. ; Fora 
description of the instrument see page 488. The new diagonal 
eye-piece of power 60 was used. 
On each night a complete determination of the clock cor- 
rection and instrumental constants was made both before and 
after the time of exchange. About 35 stars were observed 
on each night and only stars of the American Ephemeris and 
the Berliner Jahrbuch were used. The stars were so selected 
