aS 
THE 
NATIONAL GEOGRAPHIC MAGAZINE. 
Mole DT. 1890. Nowe 
ON THE TELEGRAPHIC DETERMINATIONS OF LON- 
GITUDE BY THE BUREAU OF NAVIGATION. 
By Lizut. J. A. Norris, U.S. N. 
Tue following definitions are given by Chauvenet in his Spher- 
ical and Practical Astronomy. 
“The longitude of a point on the earth’s surface is the angle at 
the Pole included between the meridian of that point and some 
assumed first meridian. he difference of longitude between any 
two points is the angle included between their meridians.” To 
describe the practical methods of obtaining this difference or 
angle, by means of the electric telegraph both overland and sub- 
marine, and especially those employed by the expeditions sent out 
by the Navy department, is the object of this paper. 
Before the invention of the telegraph various methods more or 
less accurate in their results were employed, and are still in use 
where the telegraph is not available. The one most used and 
giving the best results was that in which a number of chronom- 
eters were transported back and forth between two places the 
difference of whose longitudes was required. “For,” as the 
author quoted above says, ‘the determination of an absolute 
longitude from the first meridian or of a difference of longitude 
in general, resolves itself into the determination of the difference 
VOL, Il, L 
