162 



THE MICROSCOPE : ITS 



The introductory chapter deals with Elementary Optics. A 

 short extract from the section, which treats of Reflection, will 

 show the thoroughly practical manner in which the subject is 

 treated : — " Let us examine the course taken by rays falling on a 

 plane mirror. Let AB, Fig. 25, be the mirror, C a luminous point; 

 a ray emanating from the point, and striking the mirror at Z>, will 

 make, with the perpendicular to the surface of the mirror at that 

 point (which perpendicular is termed the normal), an angle EDF, 

 called the angle of reflection, equal to CDE^ the angle of inci- 

 dence. Other rays, CG, GN, emanating from the same point, 

 make again, with the normals GI, ///, the angles of reflection 

 IGK, JHL equal to the angles of incidence CGI and CHJ\ thus 

 all the reflected rays seem to diverge from a point C\ which has 

 no real existence, and is called the virtual image of C. Its posi- 

 tion, as compared with that of C, is symmetrical with regard to 

 the mirror." 



This section is follow- 

 ed by others on Refrac- 

 tion, Lenses and their 

 properties, Spherical aber- 

 ct ration, etc., and explained 

 by a number of diagrams. 

 Chapters IL and III. 

 describe Prof. Abbe's 

 Theory of Microscopic 

 Vision, and experiments 

 on its application. Book 

 I. treats of the micro- 

 scope, its optical parts, 

 stage, illumination, acces- 

 sory apparatus, etc., etc. 

 Here we have a good sec- 

 tional view of an objec- 

 d tive with correction collar. 

 "In 1829, Amici first no- 

 ticed that high-power 

 objectives, which give a 

 perfectly clear image 



Fig. 26. 



