The Survey of the Meridian Line. 165 
With a new transit instrument, executed by Voigt of Philadelphia, he 
ascertained the place of the star, in the tail of the constellation Ursa 
Minor, on its greatest eastern elongation, and, continuing the vertical 
circle to the surface of the ground by the instrument, he determined the 
bearing, in the line of which on a very low stand was placed one of 
Argand’s lamps covered by a tin cylinder, in which a small slit was made 
for a sight, and the line from the light toward the instrument was drawn 
upon the stand. Knowing the radius of the circle described by the star, 
or half the angle formed by its greatest elongations, east and west, and 
the altitude of the pole, he by calculation deduced the horizontal angle 
made by two vertical circles, one of which is the meridian passing through 
the pole; the other through the star’s place when farthest east. This 
horizontal angle being found, and the base line measured from the place 
of the instrument (the north door of the President’s house) to where 
it is intersected by an east-and-west line from the place of the light 
or sight used (the north side of north I street), afforded the necessary 
data for calculating the distance to be measured west from the place of 
the sight to the true meridian line, which offset was very carefully made 
and the line marked on the head of a post firmly driven into the 
ground. The meridian being thus fixed and a point found due north 
from the place of observation, the line was continued by the instrument 
at one sight and tested by reversing the telescope at an intermediate sta- 
tion in the line to the top of a hill nearly two miles north of the Presi- 
dent’s house, on the lands of Mr Robert Peter, where temporary posts 
were fixed and the line marked upon them, according to the instructions 
by signal from Mr Briggs at the instrument. From the President’s house 
the line was reversed by the instrument and continued south across the 
Tyber creek and marked in the same manner on the head of posts driven 
in the public appropriation called the mall. 
Having obtained the permission of Mr Peter, early in September I 
planted a small obelisk of freestone, prepared by Mr Blagden, in the 
meridian line north of the President’s house, on the height where the 
stakes had been fixed under the direction of Mr Briggs. The apex is in 
the true meridian from the center of the north door. 
In perpetuating the south line it was deemed best to place the stone 
where the meridian line should be intersected by a west line from the 
Capitol. The surface of the ground, however, being unfavorable—the 
Capitol not being visible at the point of intersection—it suggested the 
planting an obelisk similar to that on the north line at a point on the 
meridian west from the south end of the Capitol and where the building 
was distinctly seen, and from thence find the intersection of the center 
line by measuring northwards half the length of the Capitol. Although 
the body of the building was in full view, yet intervening trees prevented 
my seeing with the necessary distinctness the south end of the Capi- 
tol; and I had to find the required point on the meridian by setting off 
the angle included between the northwest corner of the building and 
the center of the President’s house. This angle I had previously ‘calcu- 
lated, from the distance, 7,696.8 feet, and the length of the Capitol, 351 
23—Nar, Grog. Maa.,, vor. VI, 1894. 
Sime 
