ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 409 



or shorter tube than it was specially constructed for, or to use some 

 other immersion medium than its own, water or glycerine for instance, 

 for some special purpose. Here, again, the advantage, nay, the 

 necessity, of the adjustable mounting, becomes evident. I believe 

 then that I have shown : — 



First, that homogeneous immersion has not been and is not likely 

 to be more than approximately attained. 



Second, that even if it should be fully attained, so far as the front 

 lens of the objective is concerned, the varying refractive and disper- 

 sive powers of different eyes, and different samples of cover-glass 

 would always remain to be accounted for. 



Third, hence adjustment of some kind will always be necessary. 



Fourth, that a well-made adjustable mounting for the objective is 

 the most convenient, satisfactory, and perfect arrangement for this 

 purpose yet devised. 



Fifth, that by means of such an adjustable mounting the range of 

 usefulness of an objective, as well as the convenience of using it are 

 greatly increased, and therefore, — 



Sixth, homogeneous-immersion objectives (so called or real), as 

 well as all other objectives of wide angle, should be made adjustable." 



Hitchcock's Modified Form of Vertical Illuminator.* — Professor 

 E. Hitchcock suggests another form for a vertical illuminator, which, 

 he thinks, will be better than the ordinary one, and more convenient 

 for use. 



" Instead of the reflector now used, a small glass reflecting prism is 

 placed in the nose-piece in the same way and in the same position as 

 the Wenham binocular prism, and in the case of binocular Micro- 

 scopes should replace the latter. The back surface of the prism, 

 which receives the light, may be either plane or curved ; it might be 

 found advisable to make this surface act as a lens to throw the light 

 upon the back of the objective in the most advantageous manner for 

 illumination. All parts of the prism not used should be blackened, 

 so that no light except what passes down to the objective can enter 

 the tube. A rotating diaphragm can be added, working in front of 

 the exposed surface of the prism; but this would probably be an 

 unnecessary expense."! 



Flesch's Finder.^ — Dr. Max Flesch describes the arrangement 

 shown in Fig. 74, as a simple contrivance for finding objects on a 

 slide where a more complicated apparatus is not suitable. 



A clip of horse-shoe shape attached by two pins, holds the slide 

 upon the stage. The outer sides of both arms are bevelled off and all 

 four sides graduated. When a particular object or part of an object 

 is in the field a line is drawn with a pencil along both sides of each 

 arm crossing the slide. The numbers of the divisions are also marked 

 on the slide with short cross lines, as shown in Fig. 75. If the slide 

 is again brought into its original position, as determined by the 



* Amer. Mon. Micr. Journ., iii. (1882) p. 54. 



t Mr. J. W. Stephenson informs us tiiat he had a vertical illuminator on this 

 plan constructed in 1879. 



* Arch. f. Mikr. Anat., xx. (1882) pp. 502-3 (2 figs.). 



Ser. 2.— Vol. II. ' 2 E 



