TEE> AREQUIPA STATION. 515 



stars have been discovered by Professor Pickering, Mr. H. C. Bailey 

 and the other members of the observatory. 



At the present time the equipment of the Arequipa Station of the 

 observatory consists of the following instruments: the thirteen-inch 

 Boyden telescope, an instrument so constructed that, by a change in 

 the position of the lenses, it may be used either for visual or for photo- 

 graphic work; the twenty-four-inch Bruce photographic telescope, the 

 most powerful instrument of its class in the world, a gift of the late 

 Miss Catherine Bruce, of New York ; the eight-inch Bache photographic 

 telescope; a five-inch refractor, and several smaller instruments of 

 different kinds. 



In general the work carried on in Arequipa is the extension to the 

 southern sky of that previously begun in Cambridge. This is well 

 illustrated by the Harvard photometry. With the large meridian 

 photometer alone more than a million light comparisons have been 

 made. The greater part of this work was done in Cambridge by the 

 director and his assistants, but about two hundred thousand observa- 

 tions have been made by the writer in Arequipa and elsewhere in 

 South America. This work, planned and begun by Professor Picker- 

 ing a quarter of a century ago, now furnishes not only precise deter- 

 minations of the magnitudes of all the brighter stars in the sky, but 

 also the magnitudes of certain zones of fainter stars, by which the 

 estimated magnitudes of the stars included in the various great cata- 

 logues can be reduced to the photometric scale. 



With another Pickering photometer, during the last year, several 

 thousand light comparisons of Eros were made by the waiter. Eros 

 is that remarkably interesting little planet which at times comes so 

 near the earth as to be our nearest celestial neighbor. Eros is a vari- 

 able planet, undergoing striking changes in light. The above observa- 

 tions showed that during the year 1903 the complete light-cycle was 

 only 2^^ 38™ G^.l. If these changes are due to the rotation of the 

 planet, the true period may be that given above, or, more probably, 

 twice that amount, 5^ 16™ 12s.2. 



Visual observations of variable stars have been regularly carried on 

 since the establishment of the station, although the results have not 

 yet been published. These observations are now made by Messrs. 

 Manson and Wyeth. A determination of the longitude and latitude of 

 the station was made in 1897 by Professor Winslow Upton, of Brown 

 University. The result was, longitude 4*^ 46"^ 12^ west of Green- 

 wich. The latitude is south 16° 22' 28". The longitude of the observ- 

 atory in Cambridge is 4*^ 44°^ 31^. It follows, therefore, that Arequipa 

 is about thirty miles west and four thousand miles south of Cambridge. 



Photographic work has always occupied a large share of the time 

 at Arequipa. Several photographic instruments are kept employed 



