﻿178 DESCRIPTION OF THE OBSERVATORY AT CAMBRIDGE. 



e is the situation of the standard barometer, made by Newman. 

 /, The transit or sidereal clock. 



g, The deep well, for temperature of the earth at different depths below the surface. 

 G is a building used for miscellaneous purposes, chiefly for observation of the mag- 

 netic inclination ; no iron was used in its construction. 

 H, The smaller prime-vertical room. 



D, The computing room. 



E, The observer's dwelling-house. 



The western wing, indicated by dotted lines at F, F, F", is not yet built. 



That part of the main building which is appropriated to the great refractor is 

 thirty-two feet square. The foundations of the walls are of granite blocks, which are 

 from two to three feet in thickness below the surface of the ground. Above, the 

 walls are of brick, laid in cement ; on the outside, they are carried up square to the 

 coving. Within, the» corners are arched towards the centre in such a manner as grad- 

 ually to bring the interior to a circular form for the support of the dome, leaving at 

 each of the four corners a recess five feet in depth, with a chord of eight feet four 

 inches in the lower room. In the dome room the recesses are each five feet deep, and 

 the chord is eight feet eight inches. The ceiling of the lower apartment is arched 

 inward towards the pier, but is entirely insulated from it. 



Of the four recesses in the dome, the northeastern is occupied by two closets for 

 lamps, books, apparatus belonging to the telescope, &c, and by a balance-chair, which is 

 used as a ready means of conveyance of the observer to and from the rooms below. 

 The southeastern recess contains the machinery for turning the dome. The south- 

 western is the ordinary entrance, and in the northwestern is deposited the comet-seeker 

 when not in use, with seats, table, &c, for an assistant. 



The windows of the dome are provided with iron balconies, which are found to be 

 convenient in using the comet-seeker and other smaller instruments. There is a firm 

 plank flooring to these balconies, with provision for centring the tripod-stand of the 

 comet-seeker, which brings its polar axis at once so nearly to the meridian, (the axis 

 being duly elevated to the altitude of the pole by a spirit-level,) that an object discovered 

 in sweeping may at once be referred to the large telescope. The work of adjustment 

 occupies but a few minutes, and the instrument is readily transferred from one balcony 

 to another. The floor of the dome is supported by an arched frame-work springing from 

 the walls of the building, and secured by a curb encircling, but not touching, the pier. 



Plate I., Fig. 2, is a north and south section of the foundations of the walls of the 

 equatorial and prime-vertical rooms, and of their respective piers ; at a a are the foun- 



