192 OBSERVATORY AT WEST POINT. 
western division (1), with the towers (3), (4), (5), is appropriated to the department of 
natural and experimental philosophy for purposes of instruction; and the eastern (2) 
which is in one entire room from the water table to the top of the cell, to the library. 
The first division has two floors, on the lower of which are the recitation rooms, and on 
the upper a lecture room in which is the entire apparatus, with the exception of the 
astronomical instruments. These are in towers prepared expressly for them. 
Within the towers, as will be seen by the sections, are masses of masonry, which rise 
from a bed of coarse gravel at a level twelve feet below the natural surface of the ground, 
to a height necessary to free the view from all obstruction by neighbouring obstacles. 
These walls are insulated from those around them, as well as from the floors, stair-ways 
and ceiling; and are pierced by large openings at different levels to secure a free circula- 
tion of air. Immediately to the south of the central tower, is a fourth insulated column 
(6), Fig. P, which terminates on a level near the ridge of the roof, above which the 
masonry of the enclosing wall is carried about five feet, where it terminates in a kind of 
parapet; thus forming an open space (7), Fig. R, for gazing observations, while the stu- 
dents are occupied in the use of the portable instruments, such as the smaller telescopes, 
repeating circle, altitude and azimuth instrument, sextant, &c. Access to this place 
is from the central tower, within which is a small room (9), for the safe keeping of the 
instruments just named. The mountain to the north may be seen through the door of 
communication, and an aperture in the column (10), and external wall (11), of the middle 
tower; thus securing to this position a distant meridian mark to the north as well as to 
the south. The central tower is surmounted by a travelling dome twenty-seven feet in 
horizontal diameter, and about seventeen feet high from the spring; and the surface is 
of a shape which would be generated by the rotation of a circular arc, about a vertical 
chord somewhat less than the diameter. It is pierced by five window openings near the 
curb, and an observing slit, two feet wide, extending from a point forty-eight inches above 
the floor to nearly two feet on the opposite side of the zenith. This last opening is fur- 
nished with a range of shutters of nearly equal length which are worked by means of 
levers and cords independently of each other. The whole dome rests on six twenty-four 
pound cannon balls, which turn between two cast iron annular grooves, one of which is 
inverted and attached to the curb piece, and the other to the cell walls of the tower. 
Motion is communicated to the dome by means of a rack attached to its base, and a sta- 
tionary pinion, which is turned by a hand-wheel, seven feet in diameter. 
Meridian observing slits are made in the flank towers, about twenty inches in the clear. 
These begin about two feet and a half from the floor and extend through the roof, thus 
affording an uninterrupted view of the celestial meridian from the southern to the north- 
ern point of the horizon. The design and architectural composition of the building, 
which is of the Elizabethan style of Gothic, and the effect of which is considered very 
good, is due to Major Delafield, the Superintendent of the institution. 
