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V. — Optical Curiosities of Literature. 



By the Eev. S. Leslie Bkakey, M.A. 



There is no class of artists which receives so large a share of 

 respect and admiration from their employers as the professional 

 makers of microscopes. Those who use these instruments are, 

 above all men, interested in the excellence of the performance of 

 which they are capable. They are incessantly examining and test- 

 ing them, comparing their glasses with their neighbours' glasses, or 

 the glasses of one maker with those of another maker. But the 

 qualities they are in search of depend upon conditions which are, 

 for the most part, entirely out of their reach. They can recognize 

 the finest shades of performance when they see them, but are wholly 

 ignorant of what they depend upon. As a necessary consequence 

 the makers, who hold in their hands the secrets of these things, are 

 looked up to with that peculiar awe which always attaches to the 

 mysterious and unknown. With many workers this pleasurable 

 emotion lasts to the end. I confess that, when fresh to the work, 

 I have to some extent shared this feeling ; but, less fortunate than 

 some others, have experienced the painful sensation of having my 

 eyes opened by degrees, and opened at last very widely indeecl. 

 Having been drawn on, as all workers are who really love their 

 work, to follow out some special lines of investigation, and so to be- 

 come dissatisfied with my apparatus, I used to make occasional 

 visits to London for the purpose of having it modified. In course 

 of this work I visited a great many different " houses." Acutely 

 conscious of ignorance on various points concerning the structure of 

 object-glasses, on which neither published books nor mathematical 

 calculation could throw light, I endeavoured to "improve" these 

 occasions by conversation, on the chance of picking up something 

 which might throw light on the secrets of the business. On what 

 curves depended flatness of field, — what was the difference in efiect 

 of single and triple fronts, — what was the connection between 

 " actual " focus and angle of aperture, — these and such like were 

 the things I sought to find out. 



It was this spirit of inquiry which led to the disenchantment I 

 have spoken of. Things occurred occasionally which began to raise 

 my suspicions that opticians did not always themselves know what 

 they were doing. Of my earlier experiences here is an example. 

 Having some alteration to be made in a stand-condenser, an optician, 

 well known to fame, incidentally observed that the glass was 

 wrongly made. It was double-convex, whereas such a condenser 

 " ought always to be plano-convex." It was quite essential ; and he 

 spoke with much severity of the carelessness of makers who used 

 the wrong construction. I assented, in theory at least ; and as he 



