ASTRONOMY". 47 



equipment by the trustees of the estate of the late John C. Green, 

 who founded the School of Science. 



The building is of wood, this material being chosen for the pur- 

 pose of allowing the temperature of the outside and inside air to be 

 rapidly equalized. To prevent danger from fire, all the lights are 

 from fixed gas-jets fitted with Bogarfs automatic electrical appa- 

 ratus for lighting. 



The dome is 18 feet in diameter, and is provided with a fine 

 Equatorial, by Clark, of 9^- inches aperture and about 12 feet focal 

 length. The Gaussian curves are used in the construction of the 

 object-glass, and the two lenses are so mounted that the distance 

 between them can be adjusted so as to give whatever chromatic 

 correction may best suit the work in hand, whether visual, spectro- 

 scopic, or photographic. 



The instrument is provided with all the usual micrometric acces- 

 sories, and with a Singh Prism-spectroscope by Clark, which is also 

 adapted to the use of diffraction gratings. Of these there are three, 

 with lines If inches long, the ruled space being 2 inches in width, 

 prepared expressly for this instrument by Mr. Chapman with Mr. 

 Rutherford's machine. There is also a powerful compound Spectro- 

 scopic, by Grubb, and there are the necessary electrical appliances. 



In the meridian three instruments are, or rather are to be, mount- 

 ed in separate rooms. 



The Meridian Circle is in process of construction by Fauth, of 

 Washington. Its telescope will have an aperture of 4 inches, and 

 its circles will be 2 feet in diameter, reading by four microscopes. 

 It will be provided with collimators, reversing apparatus, and ap- 

 paratus for examination of pivots. It will be mainly on the plan 

 of the instrument at the Harvard College Observatory, and will in 

 all points be a very complete and perfect instrument for purposes 

 of instruction. 



In the adjoining room is mounted a " broken"' Transit, by Kaiiler, 

 of Washington. It has an aperture of 2f inches, with a focal length 

 of 30 inches ; is fitted with a reversing apparatus, with the necessary 

 level and micrometer for latitude determinations, and with a pair 

 of collimators. 



In a third room are mounted a small Transit Instrument, of about 

 If inches aperture, and a Universal Instrument, with 8-inch circles, 

 by Buff and Berger, of Boston. 



In the prime-vertical is mounted the Aycrigg Transit, of 3 inches 

 aperture and 3 feet focus. It has an iron stand and reversing appa- 

 ratus, by Stackpole, of New York. 



At the junction of the two wings a room is formed which contains 

 a lift by which portable instruments may be taken up to the roof, 

 and used upon a platform, which is detached from the building and 



