52 Kansas Academy of Science. 



clutch throws on the load gradually, and gives a slow, steady 

 motion, so that the telescope can be kept centered on the slit. 



In order to make the observer entirely free at the guiding 

 eyepiece, the driving clock was provided with an electrical 

 winding device. The falling weight pushes a snap-switch at 

 the end of its fall and starts a small motor receiving current 

 from the 30-volt storage battery. This motor winds the clock 

 through a worm gear, and requires five minutes to do the work. 

 This makes the observer entirely free from the dome and clock, 

 so that he need not leave the eyepiece, no matter how long the 

 exposure. 



For comet and nebular photography Seed 30 plates are used. 

 An exposure of an hour and a half on the great nebula of Orion 

 will give good detail. On March 17, 1915, an exposure of 214 

 hours was made on Mellish comet, which showed the three 

 nuclei into which the comet had broken as discovered by Pro- 

 fessor Barnard five days earlier. 



Plates intended for measurement must be exposed through a 

 color filter which will transmit the visual radiations only, in 

 order to produce sharp images. This filter is made accord- 

 ing to the formula of Wallace. This has a bright yellow color 

 and lengthens the time of exposure considerably. The color 

 filter will be used to secure plates of the asteroids, the moon, 

 and for work in visual photographic magnitudes. 



Washburn College Observatory, Topeka. 



