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XVII. — On Drawing Prisms. 

 By J. Anthony, M.D. Cantab., F.E.O.P., F.K.M.S. 



{Read 11th June, 1884.) 



When tlie scientist is investigating matters of special interest by 

 means of the Microscope, he naturally wishes to record pictorially 

 what he sees, and particularly if the objects under examination 

 should chance to be of a perishable natui-e. If he has not under- 

 gone some sort of artistic training, his efforts with the pencil will 

 generally fail lamentably to convey an idea of what he sees in the 

 Microscope : his drawing will probably be utterly wanting in 

 "character," and his outlines poor and uncertain — shortcomings 

 which he will probably try to make up for by a painful elaboration 

 of detail. This is not altogether a fancy picture. A man may 

 have a most intense and learned appreciation of what the Micro- 

 scope reveals to him, and yet be utterly unable to make a reliable 

 sketch, much less a picture. It is under such cii'cumstances that 

 inventive brains have been stimulated to devise appliances which, 

 placed upon the eye-piece of a Microscope, should, by well-known 

 laws, project the Microscopic image on to a blank sheet of paper in 

 front of the observer, who would be enabled to trace with the point 

 of a pencil the outhnes and salient points of the shadowy micro- 

 scopic image. 



This is, of course, a very rude description of the general action 

 of all the mechanical aids to drawing from the Microscope, but 

 further on we shall see that special means have been devised to 

 attain special ends. 



Three questions have repeatedly been put to me. 



1 . What is the special advantage of using a drawing prism ? 



2. Does it require a knowledge of drawing to use it ? 



3. What form of prism will be the best to employ ? 



The answer ^o the first question is easy. The employment of 

 a prism means an enormous saving of time, and not only that, but 

 used with simple precautions, it means the power of delineating 

 with almost rigid accuracy the outline of all objects seen in the 

 Microscope. And this is not all the advantage, for an absolutely 

 identical magnification can be insured in every successive drawing 

 by simply marking on the Microscope a fixed observing or sketching 

 angle, and by using for succeasive sketches the same objective and 

 same ocular duly armed with the prism. As each drawing is com- 

 pleted, a simple substitution of a micrometer on the stage of the 

 Microscope allows a " scale " to be projected on to the drawing, or 

 on the side of it, which may be thus said to have received its 

 official stamp. 



Per. 2.— Vol. IV. 3 A 



