101 MOVEMENT 



the planet Venus as it passed across the sun's disc, 

 and for this purpose our learned colleague constructed 

 his astronomical revolver. This instrument contained 

 a circular sensitized plate, which at stated intervals 

 rotated through a small angle, and at each turn 



Fig. 71.— Facsimile of the print of a photographic plate obtained with the astrono- 

 mical revolver of the transit of the planet Venus across the sun, Dec. 8, 1874 (by 

 M. Junssen). , 



received a new impression on a fresh portion of the 

 plate. 



The photograph (Fig. 71) which was obtained by this 

 means consisted of a series of images arranged in a 

 circular fashion ; each image represented a new position 



