48 PICKERING— INTERNATIONAL SOUTHERN TELESCOPE. [April 18 



the prolongation of the decHnation axis of the telescope. It is here 

 enlarged by an eyepiece in the usual way. All objects on the 

 meridian, or at the same hour angle, are thus viewed by the observer 

 without changing his position. He and his recorder are enclosed in 

 a small observing room which protects them from the wind, and 

 which may be warmed if desired. When the object is near the 

 meridian, the observer is looking horizontally, and east or west. As 

 the object moves, the inclination of the line of sight gradually 

 changes, about fifteen degrees an hour. It is probable that the 

 instrument will be used principally for photographic work, and the 

 same method will be employed for following. The possibility of 

 observing a distant object in this way has been established at Har- 

 vard, since 1870, with the two eight-inch coUimating telescopes of 

 the meridian circle. The images compared in this case are nearly 

 forty feet apart. An important use of the instrument will be in 

 photographing the spectra of faint stars. These will be taken in 

 two ways. A concave and convex lens are inserted near the focal 

 plane of the telescope, and between this plane and the principal mir- 

 ror. Their positions are such that between them the cone of rays 

 -of each star is parallel. A prism is inserted as described more fully 

 in Harvard Circular 108. For measuring the approach and reces- 

 ■sion of faint stars, as described in Harvard Circular no, a similar 

 device is employed. As a large dispersion is required, the prism 

 has such an angle that the cone of rays is inclined, and comes to a 

 focus outside the tube of the telescope. The photographic plate, 

 therefore, does not intercept any part of the incident rays. The 

 reversed spectrum is formed by turning the lenses, prism, and plate 



180°. 



Cost. 



To establish an observatory of the first class is a costly operation. 

 The expenditure for plant, land, buildings, and instruments should 

 be two or three hundred thousand dollars. The annual income of 

 the Greenwich, Paris, Pulkowa, and Harvard observatories is about 

 fifty thousand dollars, in each case. To secure this permanently at 

 four per cent, the sum of $1,250,000 would be required. Accord- 

 ingly, the total cost would be $1,500,000. To duplicate the resources 

 of the U. S. Naval Observatory would involve an expenditure of at 



