38 ANNUAL RECORD OF SCIENCE AN]) INDUSTRY. 



is not improbable, however, that a series of observations of the satel- 

 lites of Jupiter, throughout its ojjposition, will be taken with the 

 Equatorial. 



An extended discussion of the declinations of 500 principal and 

 miscellaneous stars, with reductions of nearly all published series 

 of declinations to a homogeneous system, is in press. The results 

 have already been incorporated in the American Epihemeris and 

 Nautical Almanac. 



Allegheny Observatory, Allegheny, Pa. 



Professor S. P. Langley, Director. 



Replies to inquiries for information in circular of Professor S. F. 

 Baird (without date) : 



1st. Personnel of the observatory: S. P. Langley, Director ; R. F. 

 Hall, Assistant to Director. 



2d. Principal instruments: Equatorial, 13 - inch objective, finished 

 by Clark, 15 feet 8 inches focus, 20-inch hour and declination cir- 

 cles. This instrument has a considerable number of attachments 

 (besides the Filar-position Micrometer) fitting it for physical research. 

 Such are a Prism Spectroscope, of Huggins's pattern, and a more 

 powerful one using gratings ; a Polarizing Solar Eye-piece, apparatus 

 for projection, etc. An additional lens, 4 -inch aperture, of about 

 150-feet focus (by Clark), is mounted so that when used in conjunc- 

 tion with the 13 -inch objective the so-called actinic rays from the 

 central parts of the latter may be focussed together for photographic 

 purposes. 



An accessory part of the Equatorial, peculiar it is believed to this 

 instrument, has been lately added, consisting of a 12-inch Silvered 

 Plane, by Clark, mounted at the southern extremity of the j)olar 

 axis ; so that a fixed solar beam may be sent down the prolongation 

 of this axis by using the ordinary clock-work of the telescope, which, 

 thus considered, becomes a great "Fahrenheit" Heliostat; change 

 wheels in the driving-clock convert it at pleasure into an "August's " 

 Heliostat, maintaining a fixed horizontal beam. In either position, 

 heavy apparatus which could not be carried by the Equatorial can 

 be mounted on a firm support and still used in connection with the 

 telescope. 



The other instruments are a Transit of'thc English pattern, 4 inches 

 in aperture; a Chronograph ; a Sidereal Clock,by Frodsiiam; & Mean- 

 time Clock, by Howard ; an Accessory Clock, by Howard ; one Break- 

 circuit and an ordinary Chronometer, both by Frodsiiam. Besides 

 these, there are a number of minor instruments chiefly adapted to 

 solar physical research. 



:;d. The principal subjects of observation of the past year have 



