ABBE, AND MICROSCOPE THEORY IN GERMANY. 155 



of fine structures are in many cases only an indication, and 

 not a perfectly correct representation of the objects, remained 

 either unknown to most microscopists, or they looked upon such 

 conclusions as deductions from a doubtful hypothesis, which 

 might perhaps be of interest to physicists, but which could 

 in nowise fetter the living advance of the flourishing biological 

 sciences in the chains of an abstract doctrine (cp. p. 134). 

 There were even microscopists of acknowledged repute who 

 regarded the views of Abbe as totally beside the mark (cp. 

 Paper XI V., "On the Limits of Geometrical Optics"). Why 

 should one trouble one's self about such things ? If we only 

 had first-rate microscopes, what necessity to bother about the 

 path of the rays, or about the influence of diffraction on 

 the microscopic image % The reality of what was seen was 

 believed in. 



Many a controversy about fine structures, striae, etc., -would 

 not have taken place if the parties concerned had been conscious 

 that they were after all only discussing what they had seen, and 

 not that which was really present in the object itself : if they 

 had been aware that no one is in a position to tell from an 

 ever-so-sharp appearance of the image of Pleurosigma angulatum, 

 for example, what is the real construction of the siliceous frustule. 



Although within the limits of a review no space can be found 

 to enter fully into the contents of the separate treatises, an 

 attempt will be made to regard a little more in detail the more 

 important theorems — those which have a decisive bearing on 

 observations with the microscope. 



A number of papers contain essentially only descriptions of 

 new apparatus, together with the theoretical reasons which were 

 the primary consideration in their construction : e.g. Treatise I. r 

 "On a Spectroscopic Apparatus for the Microscope"; IV., "On 

 a New Illuminator " ; V., " Description of the Apertometer " ; 

 IX., " On Stephenson's System of Homogeneous Immersion " ; 

 XIII., "Description of a New Stereoscopic Ocular." 



With the exception of No. I., all the above-mentioned, how- 

 ever, stand in close connection with other treatises, which deal 

 with problems of a more general character, particularly with 

 the two most important ones : II., " On the Determination of the 

 Light Intensity in Optical Instruments" ; and III., " Contribution 

 to the Theory of the Microscope and Microscopical Observation." 



