38 



which was fitted with one plain silvered mirror and one 

 condenser as the only means oF illuraiuation then supplied ; 

 while in the present day, the means of illnminati<m are 

 thought of as much consequence as the magnifying power 

 — in fact, without the modern improved means for that end 

 the higher powers could not bo used with any effect. The 

 problem submitted to the microscopist was " Tell me all 

 about an object too small for me to see with my naked eye 

 or to touch ;" and the two things required were amplifica- 

 tion and illumination, and the first was useless without the 

 last. This was obtained in various ways. Direct and 

 oblique reflected light for opaque objects, and for transparent 

 ones direct and oblique transmitted light in addition ; — the 

 means of obtaining all which were described and illustrated. 

 The first condenser which the lecturer explained and illus- 

 trated was known as Wollaston'sdoublet, which was in use in 

 1828. Single lenses only had been used in former years, 

 and these had been found to answer to a certain extent ; 

 but an improvement took place very shortly after 

 the death of Dr. Wollaston, which inaugurated 

 a new era in microscopic illumination. The lecturer 

 described the lenses in use at this period on the black 

 board, and also showed them all to the audience -he hav- 

 ing a rare and costly collection of all sorts of articles re- 

 quired for microscopic illumination. It is impossible with- 

 out the aid of diagrams to give even a syllabus of the lec- 

 ture — suffice it to say that those who heard it experienced 

 a rich intellectual treat. The eye doublet of Dr. Wollaston 

 was shown and described at length ; and in 1831 Sir David 

 Brewster suggested a considerable improvement by making 

 the focus of the reflector fall upon the object in the plane of 

 non-aberration. A microscope with Wollaston's doublet, and 

 Herschel's lenses was shown, and, as the lecturer remarked^ 

 was deemed to be then very superior to any in use. A re- 

 markable advance from the use of single lenses took place 

 about this time (1834), so important, indeed, as to mark 

 a new era in the science of optics, as applied to miscroscopic 

 illumination, by the introduction of Ross's achromatic con- 



