50 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



Arthur Searle, A.M., Assistant. 



Leonard "Waldo, A.M., Assistant, in charge of the time-service. 



"Winslow Upton, A.M., Assistant. 



Frank Waldo, S.B., Assistant. 



Miss R. G. Saunders ; employed in reductions of the observations 

 made -with the Meridian Circle. 



Mr. Joseph F. McCormack ; employed in assisting in the observa* 

 tions made with the Meridian Circle, and in reducing them. 



There are other persons not immediately connected with the ob- 

 servatory who arc customarily employed in performing computations 

 for it. 



2d. The principal instruments of the observatory are: 



The East Equatorial, a refractor of 15 inches aperture and 22+ feet 

 focal length, made by Merz, of Munich, and mounted in 1847. 



The West Equatorial, a refractor of 5^ inches aperture and 7|- feet 

 focal length, made by Alvan Clark & Sons, and mounted in 1869. 



The East Transit Circle, made by Troughton & Slums, and mounted 

 in 1848. Aperture of telescope, 4^ inches ; focal length, 5 feet. 



The Meridian Circle. The object-glasses of the instrument and of 

 its collimators were made by Alyan Clark & Sons; the metal 

 work mainly by Troughton & Simms. The instrument was large- 

 ly designed by the late director of the observatory, Professor Joseph 

 "Winlock, and has done great credit to his ingenuity. The aperture 

 of the principal telescope is 8 inches, and its focal length 9 feet 4.4 

 inches. The aperture of each collimator is 8 inches, and its focal 

 length the same as that of the chief telescope. The instrument was 

 mounted in 1870. 



The PortaUe Transit Instrument, made by Herbst, of Pulkova, and 

 mounted in 1870. Aperture of telescope, 2f inches; focal length, 

 33 inches. 



3d. The work done with the Equatorials has principally con- 

 sisted of photometric observations of the brighter double stars (in- 

 cluding, in the case of some colored stars, measurements of the va- 

 riations of their light in different parts of the spectrum) ; of faint 

 stars used as test-objects; of the satellites of the superior planets; 

 and of the eclipses of Jupiter's satellites, thus determining the times 

 of these eclipses more accurately than by the usual method. Among 

 the miscellaneous observations made may be mentioned measure- 

 ments of the diameter of Mercury during its transit, and determina- 

 tions of the positions of asteroids. 



The Meridian Circle has been employed, first, in completing the 

 observation of the zone 50 to 55 north declination, undertaken by 

 this observatory as its contribution to the work of determining the 

 places of the stars of the ninth magnitude, or brighter, belonging to 

 the northern hemisphere; secondly, in observing, at the request of 



