Celestial Photograph!/ — WasJibuni Telescope. 51 



satellite keeps the same face towards the planet during its 

 revolution and that the marking is always turned away. It 

 would be interesting to see if this feature is a permanent one at 

 the coming October opposition, which will be the nearest ap- 

 proach of the planet in twelve years. 

 Washburn College Observatory, Topeka. 



CELESTIAL PHOTOGRAPHY WITH THE WASHBURN 



TELESCOPE. 



Edison Pettit. 



TOURING the past year preparations were made to adapt 

 ^-^ the Washburn College refractor to celestial photography. 

 Some preliminary attempts showed that the telescope, which 

 has an llV^-irich Brashear objective, was capable of produc- 

 ing good photographic images. With this in view, a double- 

 slide plate holder was built in the college shop, which makes ac- 

 curate guiding possible. 



A brass collar fits over the 41/2-inch draw tube, and to this is 

 attached a brass plate which may be rotated in position angle. 

 To this plate is attached the double-slide plate holder with guid- 

 ing eyepiece and shifting screws. A plate-carrier opening in 

 the back provides means of bringing the lilm to exact focus. 

 The cross wires are No. 60 copper and illuminated with a 

 flash-light bulb which receives current from the 11-volt a. c. 

 telescope circuit, and may be adjusted through a potentiom- 

 eter. The carrier takes 3 by 31/2 in. plates. 



With this form of plate holder the guiding is done on the 

 same field of stars that is being photographed, and the correc- 

 tions to the clock motion are made by shifting the whole plate 

 and not the telescope. The field having been selected, a guiding 

 star is found and set on the cross wires, a plate cut and in- 

 serted, and the slide cover drawn. The star is now kept on 

 the cross by manipulating the two shifting screws, which move 

 the plate in two directions at right angles to each other. 



To facilitate photographic and other astronomical work the 

 dome has been provided with a 1/2 hp. a. c. motor for revolving 

 it. The starting box and reversing switch are placed on the 

 side of the observing ladder, so that the observer need not leave 

 the guiding eyepiece to shift the dome. A centrifugal friction 



