ASTRONOMICAL OBSERVATORIES. 233 



In December, 1849, the use of the electric clock was 

 introduced at the Washington observatory, and the 

 original method of observation was somewhat modified. 

 In the west transit instrument was inserted a new dia- 

 phragm, having two systems of wires which included 75 

 spider-lines, viz., one system of vertical and one system 

 of inclined wires. Each system is divided into groups 

 of five wires each. By observing the transit of a star 

 over a group of vertical wires, its right ascension is de- 

 termined ; and by observing its transit over a group of 

 inclined wires, the difference of declination between this 

 and other stars similarly observed may be computed. All 

 these observations are recorded on a fillet of paper by 

 means of an electric circuit, by simply pressing a key 

 as the star is seen to pass each of the wires of the transit 

 instrument. 



Three quarto volumes of Washington observations have 

 been published, viz., the observations for 1845, 1846, 

 and 1847. 



The volume for 1845 contains 550 pages, and ftirnishes 

 a full description of the instruments employed, illustrated 

 by numerous engravings. It also famishes a large num- 

 ber of observations with the transit instrument, the 

 mural circle, and the prime vertical transit. The volume 

 for 1846 contains 676 pages, and besides observations, 

 with the instruments used in 1845, furnishes also ob- 

 servations with the meridian circle and equatorial. All 

 these observation are .carefully reduced, and the places 

 of the sun, moon and planets, are compared with their 



