6 PRESIDENTIAL ADDRESS. 



that the bad ones will be driveii out of the market, as a good 

 eye-piece is necessary to do justice to an objective. Another 

 advantage of the abolition of the secondary spectrum is that the 

 lenses so constructed can be used for photography without the 

 guess-work of altering the adjustment so as to bring the chemical 

 rays into focus. Mr. Zeiss has brought out a projection eye-piece 

 to be used in this work, but I have not tried it yet, so cannot give 

 any opinion about it. This art of photo-micrography is one which 

 has lately made rapid advances, but is still in its infant stage. To 

 those of our members who want employment for long winter 

 evenings I can highly recommend this branch of microscope work, 

 especially as certain improvements in photography have made it 

 more satisfactory. Everyone knows the advantage of a photo- 

 graph, as it keeps a permanent record of one's work, which is free 

 from the suspicion of being largely dependent on the imagination 

 (a suspicion to which drawings are always liable). Most observers 

 draw what they Avish to see rather than what is actually seen. 

 Besides having once got the negative, it is an easy matter to get 

 any number of copies from it. 



To glance at the technical part of photo-micrography, good 

 rapid dry-plates are generally considered the best to use, and from 

 these copies and enlargements can always be made. Jiowever, I 

 am inclined to think that paper will be the coming thing for 

 microscopists, and the following method might be made practic- 

 able, as the camera would not get rough usage : — Attach a simple 

 and light roller-slide of small proportions to a very light conical 

 camera, carrying at the end opposite the roller-slide either a pro- 

 jection eye-piece or else a simple tube, so marked that the image 

 would be always properly focussed on the sensitive surface, and 

 if this camera was so arranged as to take the place of the eye- 

 piece when required, the niicroscopist could keep it near him 

 while at work, and in a few minutes could shift it for the eye-piece, 

 and take a photograph of any interesting object, developing the 

 image at his leisure. He would thus soon acquire an interesting 

 and valuable set of photographs. Now, if paper was used, there 

 would be often no need for printing at all, as the negative could 

 be placed in his album. The printing is often a most important 

 point, and if the negative is large enough to be satisfactory and 



