8Q PHOTO-MICROGRAPHY. 



those higher than the h inch, an achromatic condenser will be 

 required. 



From the foregoing, it will be seen that Photo-Micrography 

 and Photo-Enlarging are as nearly as possible identical operations ; 

 in fact, I have obtained in this way several fairly good pictures of 

 the larger microscopic objects, mounted by Enock, such as Larva 

 of Vapourer Moth, Orgyia aiiticjiia — Fan-Tail Fly, Dolichopus 

 nohilitatiis — Green Saw-Fly, Tenthredo Viridts, etc. If it is 

 intended to make transparencies for the Lantern from the Micro- 

 Negatives obtained, I recommend the carbon process : it is not 

 difficult, and the results are very superior. The tissue is suppUed 

 by the Autotype Company. 



Dr. Koch, of Berlin, has sent some Photo-Micrographs to 

 Professor Lister, of King's College, which far surpass anything 

 that has hitherto been done : they are pictures of some of the 

 minutest living organisms, and were executed, I believe, to illustrate 

 the germ theory of disease. They were exhibited at the Inter- 

 national Medical Congress recently held in London ; and I 

 append a few details of his mode of working, copied from " The 

 Photographic News." He uses an immersion lens, by Siebert 

 and Kraft, of Wetzlar, and for illumination employs sunlight 

 reflected by means of a heliostat. A wide-angled condenser 

 concentrates the light, which is passed through an ammoniacal 

 solution of copper, rendered as monochromatic as possible, and 

 then diffused and softened by allowing it to pass through ground 

 glass. He works with wet collodion, and finds that an exposure 

 of two minutes suffices in the case of an enlargement of seven 

 hundred diameters. 



I have endeavoured to make the foregoing article as plain and 

 simple as possible, remembering that my own early attempts at 

 Photo-Micrography were attended with many difficulties and 

 failures ; for all the articles which I read bearing upon the subject 

 were so utterly unpractical, or so highly scientific, that a beginner 

 could glean from them but little information of any real value. 



