3l8 THE SCIENCE OF MICROSCOPY. 



question, as it implies some kind of scientific discipline, unless 

 indeed it simply means — as it too frequently may — that the 

 microscopist does not suspect his own mistakes ! And the fact 

 remains — however accounted for — that errors of observation have 

 been made and accepted, until the narrative occupies the longest 

 chapter of "revelations ' for which the microscope has been made 

 responsible, proof enough that an wwreasoning trust in micros- 

 cope observations is but leaning upon a broken reed. For the past 

 history of microscopy exhibits a record of contradictory, and in great 

 part fruitless observations, which would be' indeed discouraging if 

 there was no hope that the interpretation of optical rule would in 

 time supersede the dicta of individual conviction. Errors of fact 

 ever and again corrected and re-corrected ; opinions refuted and 

 recanted ; theories set up only to be demolished ; studies mis- 

 directed by the truthful seeming of what proves to be illusion : 

 these are mis-adventures of '' practical microscopy'' in full posses- 

 sion of an instrument admitted to be "par excellence" an 

 instrument of precision, but manipulated by workers guiltless of 

 the restraint of optical law. And this history repeats itself with 

 proverbial monotony amidst the perpetual announcements of fresh 

 " revelations.'' 



Is, then, the instrument or the worker at fault ? 



In defining the optical theory of the microscope, theory has 

 shown precisely how the microscope image is formed, and what is 

 imaged, and has proved by analytic methods of its own what are 

 and must remain its limits of performance, as well as how nearly 

 these have been reached. So far, therefore, it has vindicated the 

 title of the microscope to be considered an instrument of precision. 

 But theory also teaches us that the interpretation of appearances 

 revealed in the microscope image must be based on the considera- 

 tion that this image expresses optical effects consequent upon a 

 variety of physical antecedents, besides those which originate in 

 the object 3 whilst on the other hand material details, truly existing 

 and working in the object, are not always indicated by effects 



