CHAPTEK XXII. 

 LANTERN SLIDES. 



It is almost beyond question that the most useful, imposing 

 and satisfactory method by which we can exhibit to others the 

 result of our micrographic work, lies in the projection of a posi- 

 tive image upon a white, and proportionately large, surface called 

 the " sheet " or " screen," by means of an Optical Lantern. 



So strongly does the writer feel the importance of this subject 

 that he proposes to devote a chapter to a plea for the use of 

 the Lantern for many purposes. The present chapter will be 

 devoted to a description of certain processes which seem to 

 the writer most suitable for slide-making in the hands of those 

 who are not thoroughly conversant with this branch of photo- 

 graphy. 



It is necessary in the first place to know precisely what 

 qualities we require to obtain in a slide so that it may be a 

 thoroughly good slide, or as nearly perfect as our subject 

 and our negative will allow. 



The first attribute to a slide, specially of a photo-microgra- 

 phic slide, is perfect clearness of the ground. Wherever there 

 is no subject the glass must be quite clear. A good slide laid 

 down on a sheet of white paper, will show the paper, seen 

 through the ground of the slide, perfectly white. There 

 should in such condition be no graying or degradation of the 

 purity of the white in the paper. 



The image may be of various tones according to the process 

 used, but it must always be " plucky," and never pale or 

 " washed out," the details must stand out clearly from each 

 other, as if etched with the finest needle. A perfect slide is 

 indescribable but once seen will never be forgotten. 



The image, though plucky, must not be opaque, except 

 where the detail in the microscopic image was opaque. Such 



