154 Transactions of the 



man, and any competent observer can judge of the quality of this 

 portion of the work, by examining the pictures themselves. The 

 microscopist who directs the work is best employed in seeing the 

 object, which, if he foUows the simple methods I have described in 

 previous papers, will secure an image, of all he sees, on the sensitive 

 plate ; but nothing more. There is no charm in photography which 

 can make it a touchstone of truth. If the objectives are imperfect ; 

 if the illumination is faulty ; if the object is dirty or improperly 

 prepared, the photograph will tell the whole story as no drawing 

 or description would do. Others will be in a position to judge the 

 faults of the microscopist's work, and this by the way is no doubt 

 one reason why so many observers shrink from the cruel sincerity 

 of this method of representation. When our improved objectives 

 first showed the markings on the Angulatum as hexagons, photo- 

 graphy faithfully reproduced them. When higher powers of better 

 definition showed the hexagons to be imperfectly seen circles, 

 photography had no difficulty in representing these. The hemi- 

 spheres rendered visible by a still further advance are shown in the 

 photographs which accompany this paper, and any future progress 

 resulting from better optical apphances will be chronicled in the 

 same manner. 



It is sometimes thoughtlessly objected that photo-micrography 

 reproduces the phenomena of interference or diffraction, as well as 

 the real structure. This I readily admit, and claim as an advantage, 

 for these phenomena are actually seen by the observer. If he merely 

 describes or draws, he omits all that he supposes belongs to this 

 category, and by so doing omits sometimes the essential ; the photo- 

 graph omits nothing, and anyone who examines it is placed more 

 nearly on the plane of the original observer than he could be by any 

 other means, unless indeed he could sit by the observer's side and 

 look over his shoulder. This first limitation of the interpretation 

 of micro-photographs, therefore, is in fact only a guarantee of their 

 optical honesty. 



There are other and different limitations, however, which require 

 mention. Thus our efforts to represent opaque objects, particularly 

 as seen with medium and high powers, have not as yet been crowned 

 with any great success. How far this results from the small amount 

 of labour hitherto expended in this direction, is not to the purpose ; 

 the success is not yet attained. So also there are certain yellow 

 objects, such as parts of insects, for example, which transmit so little 

 violet light that as they are ordinarily prepared, photography fails 

 to exhibit all the details discernible by the eye. This difficulty, 

 however, is readily escaped by resorting to suitable bleaching pro- 

 cesses in the preparation of the objects, and these very processes 

 greatly improve the character of the objects for observation by 

 the eye. 



