104 THE VICTORIAN NATURALIST. 



lithographic printing. I am told that by a new process copies 

 can be produced from a photo-micrographic negative at the rate 

 of some thousands per week, each one of them superior in detail 

 to the ordinary photographic print, and preserving exactly the 

 accuracy of the negative. 



Photography, too, is true. When examining a delineation of a 

 microscopic specimen obtained by this means, you may feel 

 satisfied that it presents, at least, one aspect of the object. It is 

 a truthful rendering of what the microscope has actually 

 enlarged ; and says Dallinger, in his work on the microscope : — 

 " It must be remembered that photo-micrography, by constantly 

 covering a wider area of application with its ever increasingly 

 delicate and subtle methods, is more penetrating in its revelation 

 of structure than the human eye." 



Photo-micrography is an amalgamation of microscopy and 

 photography. A lifetime of study is not too long to exhaust 

 either of these subjects ; and, necessarily, while many men are 

 well equipped in one, the number of those who are thoroughly 

 versed in both is very small. It will not suffice, however, to be a 

 microscopist with only a smattering of photography ; but to 

 excel in photo-micrography one must be conversant with both 

 subjects. Before commencing this work with any hope of 

 success, one must make himself thoroughly acquainted with the 

 optical and mechanical parts of his microscope ; and in addition 

 to the ordinary photographic processes he must also familiarize 

 himself with the great variations in exposure requisite under 

 different conditions, as, for instance, upon different lengths in the 

 extension of his camera, the different powers applied to the 

 microscope, and the degree of opacity and the sensitiveness of 

 colour of the objects to be photographed. 



We must now pass on to the practical portion of our subject,, 

 and first of all we will decide what instruments and apparatus 

 are necessary for photo-micrography. 



I shall not take up your time by describing the more com- 

 plicated instruments devised for this work, my object being more 

 particularly to refer to apparatus in reach of all, and by means of 

 which first-class photo-micrographs can be produced. 



In regard to the microscope stand, this should be a good solid 

 one, and extremely rigid. Photo-micrography with high powers 

 demands the greatest convenience in the adjustments, and the 

 very highest excellence in the mechanical parts of the apparatus 

 employed. The microscope should have diagonal rack and 

 spiral pinion to the coarse adjustment, and an efficient fine 

 adjustment. With some fine adjustments it will be found that the 

 appearance of an object left focussed for a minute or two will have 

 slightly varied ; so that it will be readily perceived that as photo- 

 micrograplis frequently require one hour exposure, it is very 



