ASTPOXOMY. 47 



Fifth, the principal publications of the year. 



It was intended that one such circular should reach every 

 observatory, public or private, in the United States. If any 

 have been omitted, it has been by inadvertence, and notice of 

 such omissions is desired by the editor. 



The various replies to this circular follow in the alphabet- 

 ical order of cities, and are given unchanged, except that oc- 

 casionally material elsewhere accessible has been omitted to 

 gain space. 



It is proposed to continue these summaries in the future, 

 and it is hoped that the directors of the various institutions 

 will be willing to furnish from year to year brief sketches of 

 the activity of the observatories under their charge. In this 

 way a record of current astronomical work in the United 

 States will be kept up, which otherwise it is difficult to main- 

 tain in the absence of any American periodical specially de- 

 voted to astronomy. 



Allegheny City, Pa. : Allegheny Observatory. 



Professor S. P. Langley, Director. 



1st. The Allegheny Observatory is under the charge of the direc- 

 tor, Professor S. P. Langley, who is aided at the present time by Mr. 

 F. W. Very. 



2d. Its principal instruments are an Equatorial, made by H. Fitz, 

 of New York, the object-glass of which has been refigured by Alvan 

 Clark & Sons, of Cambridge. It has an aperture of 13 inches, and 

 is provided with hour circle, reading to seconds of time, and decli- 

 nation circle, reading to 10" of arc ; Position Micrometer, Polarizing 

 Eye-piece, and spectroscopic attachments. One of the spectroscopes, 

 constructed by H. Grunow, of New York, is provided with a special 

 arrangement for reflecting light from two independent sources into 

 the slit, which is so adjusted that the line of division between any 

 two parallel spectra becomes nearly invisible. As an instance of its 

 application, when the light from opposite ends of the sun's equatorial 

 diameter is examined, the Fraunhofer lines of solar origin are seen to 

 be discontinuous in the two spectra, when the terrestrial atmospheric 

 lines are exactly prolonged from one spectrum into the other, and this 

 affords a method of discriminating between solar and telluric lines 

 which promises good results. There is a Spectroscope with two 

 prisms, after Huggins's pattern, made by Troughton & Simms ; but 

 the more powerful instruments are supplied with Mr. Rutherfukd's 

 gratings. 



The lower end of the polar axis of the Equatorial carries an opti- 



