ASTRONOMICAL OBSERVATORIES. 231 



four feet diameter, one on each end of the axis, divided 

 on gold into arcs of two minutes. Each circle is pro- 

 vided with six reading microscopes. The telescope has 

 two micrometers, one moving in azimuth, the other in 

 altitude. 



The comet-seeker was made by Merz and Mahler. 

 It has an object-glass of about 4 inches in diameter, 

 and with a focal length of 32 inches, with which low 

 magnifying powers are used, that it may embrace a large 

 field, and collect the greatest possible quantity of light. 

 The cost of this instrument was $280. 



In the fell of 1844, Lieutenant Maury was directed to 

 take charge of the new "Depot of Charts and Instru- 

 ments." Lieutenant Maury commenced a regular and 

 systematic series of observations upon the sun and moon, 

 the planets, and a list of fundamental stars, comprising 

 those of the greatest magnitude and of the most favorable 

 positions, to be used as standard stars. He also under- 

 took observations for a most extensive catalogue of stars. 



This work contemplates a regular and systematic ex- 

 amination of every point of space in the heavens that is 

 visible at Washington, and of assigning position, color, 

 and magnitude to every star that the instruments are 

 capable of reaching. The following plan of sweeping 

 was adopted : The telescope of the mural circle is set 

 in altitude, and all the microscopes carefully read and 

 recorded, and the eye-piece is moved up and down so 

 as to cover a belt of about 50 minutes in declination. 

 The micrometer diaphragm is provided with a number 



