ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 651 



the aperture was being diminished was most suggestive. The object 

 was fairly well seen until the aperture became rather small, but then on 

 further contraction of the aperture a succession of new phenomena 

 sprang into existence, until at a certain stage the appearance became 

 that represented in fig. 114, and was then utterly unlike the real object. 

 The semicircle has disappeared, and instead of it and the one straight 

 canal across the triangle, we have what appear to be three canals 

 of nearly equal thickness, and abutting nearly perpendicularly upon 

 the three sides of the entire triangular space. And at the same 

 time "carets" have developed themselves at the outer ends of these 

 three optically-produced canals. These unsteady appearances, which 

 sometimes metamorphose an object into something utterly unlike 

 itself, are of the same kind as those by which the astronomer, who 

 occupies himself upon minute details, is but too likely to be misled, 

 unless he avails himself of some such aids as those which the author 

 has ventured in his memoir to recommend. [In looking at fig. 114 

 the reader is requested to exercise his imagination, for none of the 

 features as seen in the Microscope had the hard outlines of the diagram. 

 The three " canals " were dusky streaks with straight but nebulous 

 edges, and the boundary of the triangular bright space was also 

 nebulous. The " carets " were the darkest part of the image.] 



Royal Microscopical Society's Microscopes at the Franco- 

 British Exhibition. 



The Royal Microscopical Society contributed, as announced at the 

 May Meeting of the Society last year, a collection of Microscopes to the 

 British Science Section of the Franco-British Exhibition. The collec- 

 tion was illustrative of the development of the Microscope from the 

 earliest times, and comprised, in addition to twenty-three instruments 

 belonging to the Society, four which were lent by Fellows : two by 

 Sir Frank Crisp and two by Mr. E. M. Nelson. 



The collection was distributed into five groups as follows : 



1. Simple Microscopes. 



2. Compound instruments of the Scarlet and Culpeper type, in which 

 the lenses are carried in a body which slides in a ring for the purpose 

 of focusing, and in which no attempt is made to obtain achromatism. 



3. Instruments of a more highly developed type, in which screw 

 motions are introduced for the purposes of focusing and the instru- 

 ments were what was at the time called the universal type, that is to say, 

 were adapted to be used either as simple or as compound instruments, 

 and fitted for the observation of opaque or transparent objects under 

 various conditions of stage and illumination. They, however, are non- 

 achromatic. 



4. The Catoptric type, in which an attempt was made to get over the 

 difficulty of achromatic aberration by substituting mirrors for lenses 

 in the objective. This type of instrument was represented by a single 

 specimen (Cuthbert's reflector Microscope). 



5. The group of achromatic Microscopes, leading up, in their full 

 development, to the modern instrument. 



The following is a descriptive list of the instruments exhibited. 



