ASTRONOMIC^ OBSERVATORIES. 227 



a clock regulated to sidereal time. Immediately east of 

 the observatory is the dwelling of the superintendent. 



The great refracting telescope was made by Merz and 

 Mahler, of Munich. The object-glass has a focal length 

 of 15 feet, and an aperture of nine and a half inches. 

 This telescope is equatorially mounted, and furnished 

 with clock-work. It has a repeating filar micrometer, 

 with eight eye-pieces, magnifying from 100 to 1000 times. 

 The cost of this telescope was $6000, its object-glass 

 alone being valued at $3,600. 



The transit instrument has an object-glass with a clear 

 aperture of five and a half inches, and a focal length of 

 88 inches, furnished by Merz and Mahler, and the in- 

 strument was constructed by Ertel and Son, of Munich. 

 It is mounted upon large piers of granite, which rest 

 firmly on a foundation of stone, extending ten feet below 

 the surface of the ground. The cost of this instrument 

 was $1480 ; the object-glass alone cost $320. 



The mural circle was made by Mr. William Simms, of 

 London. It is five feet in diameter, made of brass, and 

 cast in a single piece. It is divided into spaces of five 

 minutes each, upon a band of gold inlaid on the rim, or 

 perpendicular to the plane of the circle. Placed at equal 

 distances round the circle are six micrometer microscopes, 

 with an acute cross of wires at their foci, for reading 

 angles less than, five minutes. Five revolutions of, the 

 micrometer are designed to measure five minutes upon 

 the circle. The micrometer heads being divided into 

 sixty equal parts, each division represents one second of 



