A DESCRIPTION OF A NEW PHOTOGRAPHIC TRANSIT 



INSTRUMENT. 



By frank SCHLESINGER. 



(Read April is, IQI?-) 



A camera lens of wide field is mounted at one end of a rigid tube 

 built up of small angle irons. At the other end is the plate carrier. 

 Adjustments for collimation, base and focus are provided. On the 

 under side of the tube not far from the objective is a ball which fits 

 into a socket mounted on a pier, and these form the polar axis of the 

 instrument. The lower end of the tube rolls on a glass plate attached 

 to the same pier, the latter pointing to the intersection of the celes- 

 tial equator with the meridian. To the camera is attached a driving 

 clock regulated to the sidereal rate. The glass plate is adjusted to 

 the celestial equator and in this way round star images are obtained 

 on the photographic plate. Near the lower end of the camera is 

 attached an electric contact which operates on a hinge without lost 

 motion. As the driving clock moves the camera across the meridian 

 this contact falls by its own weight into a number of slots in succes- 

 sion, cut into a brass rod that forms the other terminal of an electric 

 circuit. In this way we obtain upon a chronographic sheet eight 

 sharp and short signals every minute. The same circuit contains a 

 sidereal clock and thus we have the means of finding at what times 

 the camera passed the slots in the brass rod. 



The method of observation is as follows: two or three minutes 

 before a certain group of equatorial stars comes to the meridian, the 

 driving clock is started and the lens is uncovered just before the 

 contact falls into the first slot. The exposure lasts say five minutes, 

 the camera being covered just after the contact has passed over the 

 last slot. Without disturbing the plate in any way the camera is 

 moved back to its original position so as to point again a few minutes 

 east of the mcridinan. Some time later the process is repeated on 



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