40 PRACTICAL PHOTO-MICROGRAPHY. 



In Great Britain, at all events, the use of direct sunlight may 

 be set aside as not available, certainly as not presenting suffici- 

 ent advantages to counteract its enormous disadvantages, and 

 in America there is no longer the necessity for it that there 

 was in the days of Woodward's achievements. No work on 

 photo-micrography, however, could pretend to be complete 

 without something more than an allusion to sunlight illumina- 

 tion, so we shall present a diagram of the arrangement used by 

 Woodward, an arrangement which in many respects formed 

 the basis of future developments. 



Messrs. Truan and Witt, in the production by wet collodion 

 of a fine series of photo-micrographs representing certain Dia- 

 tomaecse of Hayti, used an apparatus wherein direct sunlight 

 was projected by means of the mirror of a Chevalier megascope. 



Dr. Woodward, after using the arrangement figured 

 No. 10, made alterations which he considered improvements 

 and which in some respects undoubtedly were steps in the 

 right direction. He used a room as his camera, supporting his 

 sensitive plate on an easel which was made to run on rails to 

 and from the microscope which, with objectives, was fixed to 

 the window shutter, the light, as before, being reflected 

 through the optical system by a heliostat. The obvious disad- 

 vantage of this arrangement was the fact that in case of any 

 tremor the sensitive plate and the optical system might not 

 move together. Dr. Maddox used also a darkened room, but 

 he had in the room a camera, reflecting the sunlight by means 

 of a mirror and prism through the optical system which was 

 fitted to a hole made in the shutter. Non-actinic light was ad- 

 mitted into the room by means of suitable " light-filtering " 

 media. Many other arrangements might be mentioned with- 

 out any notable difference from or superiority over these 

 already touched. 



An important feature in sunlight illumination is the use 

 of " monochromatic " light. The reader .is probably aware 

 that the rays composing a beam of white light are not all 

 equally energetic in producing the chemical action necessary 

 to the production of a photographic image. The waves of 

 light producing the sensation of sight vary in length from 



