﻿183 DESCRIPTION OF THE OBSERVATORY AT CAMBRIDGE. 



Fig. 5 of the same plate is a section of the northern shuttei, where the same parts, 

 acting in a similar manner, are indicated by the same letters, accented. This part moves 

 independently of the southern, and has a like arrangement for opening and closing, only 

 that the two open in opposite directions, one east and the other west. 



This plan has been found to answer completely the intended purpose. The shutters 

 are perfectly weather-proof, and the division into two parts, by keeping the northern part 

 closed during high and cold northerly winds, affords comfort to the observer and protec- 

 tion to the instrument. The southern opening has a range of 110°. 



The lesser equatorial is mounted in a detached building, situated about two hundred 

 feet northwest of the great central pier. This building is of wood, and twelve feet in 

 diameter ; it turns on iron balls of six inches in diameter, moving in hollow, cast-iron 

 ways. It is turned by hand, without any machinery. The telescope has an object-glass 

 of four and an eighth inches diameter, by Merz, and sixty inches focus, and is provided 

 with spider-line, double-image (Airy's), and annular micrometers. The mounting is by 

 Simms, and its support a granite pedestal entirely isolated from the building. 



The comet-seeker is by Merz, and is equatorially mounted after the German fashion. 

 It is portable, and is used from the balconies of the dome ; the aperture of its object-glass 

 is four inches, and its field of view four degrees. 



A transit instrument of four feet, made by Troughton & Simms, is mounted on 

 granite piers, in the meridian at a, Plate I., Fig. 1. It has also been occasionally used as 

 a prime-vertical instrument on the pier in the room c, an extra pair of Ys being provided 

 for it for that purpose. 



An eighteen-inch variation transit, or altitude and azimuth instrument, is placed on a 

 wooden tripod at a. This is used in the adjustment of the magnetic apparatus, which 

 consists of a Lloyd declination-magnetometer at c, and a horizontal-force bifilar mag- 

 netometer at b. 



Besides the above, the Observatory is furnished with four four-foot achromatic, and 

 two reflecting telescopes, the necessary apparatus for meteorological observations, an as- 

 tronomical clock, and several sidereal chronometers. 



It is proper to add, that the necessary funds for the establishment of the Observatory, 

 and for its permanent endowment, have been furnished mainly through the liberality of 

 private citizens of Boston and its vicinity. The expense of the buildings and grounds 

 has been defrayed by the University. 



