ON THE THEORY OF THE MICEOSCOPE. 203 



the theory which enables us to give a sufficient account of the 

 mode of action of a microscope when it is made, does not at the 

 same time serye as the foundation of its construction ? Why do 

 we not construct this kind of optical instrament by help of 

 calculation founded on theoretically deduced formulae as has been 

 so successfully done since the time of Prauenhofer for the 

 telescope, and in more recent times for the optical part of the 

 photograph-camera P"*' 



* In corroboration of the fact here alluded to as currently accepted in 

 Germany, tbe following extract from Lardner's " Cbapter on the JMicros- 

 cope," (paragrapb 11) in his Museum of Science, may find a suitable place 

 as shewing the same fact from an English point of view. 



" Now the solution of this problem presented to scientific and practical 

 men the most enormous diflSLculties — difficulties so great as to have 

 been regarded by some of the highest scientific authorities of 

 the last half century as absolutely insurmountable. Happily, never- 

 theless, the problem has been solved; (!) and without disparagement 

 to the great lights of science, we must admit that its solution 

 has mainly been the ^ork of practical opticians. It is true that 

 the general principles upon which the form and material of the 

 lenses depend, were the result of profound mathematical research; but 

 these principles were established and well understood at the moment when 

 the practical solution of the problem was by scientific authorities them- 

 selves pronoxmced to be aU-but impossible. Opticians, stimulated by 

 microscopists and amateurs, then applied themselves to the work ; and by 

 a long series of laborious and (costly trials, attended with many and most 

 discouraging failures, at length arrived at the i^ro duction of optical com- 

 binations which have rendered the microscope one of the most perfect 

 iastruments of philosophic research, and one to the increasing powers of 

 which we can scarcely see how any limit (!!) can be assigned." 



The historical truth of Dr. Lardner's statement is not afl'ected by its 

 being somewhat out of date ; on the contrary, it remains vahd for the years 

 intervening between that date and the present time. We still look for an 

 adequate scientific theory of the microscope in our present micrographic 

 hterature. And the rules and methods of construction now employed in such 

 optical combinations as the microscope objective, are known only to those 

 who have made personal sacrifices of time, study and money to attain it. In 

 a word, the most successful and important achievement of optical science is a 

 trade secret. It is scarcely possible to urge a stronger proof of the value 



