16 INTRODUCTORY ADDRESS: 



years before Oil Immersion Objectives were constructed at Jena hy 

 Professor Abbe. In a Paper read by Mr. Wenham, entitled "Remarks 

 on High-power Definition," at a meeting of the Royal Microscopical 

 Society in June of that year 1870, he says : "Of course there is 

 no optical advantage attendant upon the use of water in immersion 

 lenses. If a medium of the same refractive power as the glass were 

 to be emj^loyed the result would be better. Water, having a low 

 refractive index, an adjustment is required for each thickness of cover, 

 and a difference of adjustment is not so marked and sensitive as in the^ 

 ordinary dry objective ; but if a medium of similar refraction to the 

 glass were to be used, no adjustment would be required for any thick-, 

 ness of cover, supposing the test obj ects to be mounted thereon (which 

 they generally are), for, in fact, we should then view them all with a 

 front of the same thickness — considering the cover, the front lens and 

 the interposing medium as one." 



In addition to reading this Paper, Mr. Wenham exhibited at the 

 same Meeting an Oil Immersion Lens using Cedar Oil and an illuminated 

 object showing great brilliancy. It appears, however, he did not 

 at the time realise that his Oil Immersion could have yielded the great 

 numerical aperture which it afterwards gave in the hands of Professor 

 Abbe. 



Another interesting point is the fact that Andrew Ross, the founder 

 of the firm of Messrs. Ross, discovered the system of the Collar 

 Adjustment for Water Immersion Lenses and that Mr. Wenham 

 was the Discoverer of the Oil Immersion which required no Collar 

 Correction. 



To show how little was thought of the Microscope as a scientific 

 instrument in connection with the study of Iron and Steel, reference 

 may be made to a Book which I have often found useful, namely^ 

 Ferdinand Kohn's " Iron and Steel Manufacture," published about 

 1868 and based upon a series of valuable articles on " The Manufacture 

 of Iron and Steel," which appeared in " Engineering." In this 

 book Kohn says, in the chapter devoted to " Steel under the 

 Microscope," "An experienced steelmaker can estimate very closely the 

 ferrous quality, chemical composition, tensile and compressive strength 

 of any sample of steel, and even the mode of treatment which it has 

 undergone, by looking at its fracture under the Microscope." 



It appears, however, this only meant a small hand Microscope. The 

 following are the words : "A Pocket Microscope of this kind ought to 

 be the companion of every man interested in Steel or Steel Manufacture. 

 Lenses of the usual kind, even if piled up in sets of three or four, are 

 entirely insufficient. The Lens must be of a very small focus, and 

 properly achromatic. A little practice is sufficient to enable the user 

 to " see " through this Lens ; but it is, of course, not quite so easy 

 to learn the meaning of what is seen, and to estimate from the appear- 

 ance the quality of the steel inspected." 



Special reference was made to some investigations then being 

 carried out (1868) by Mr. Schott, the Manager of Count Stolberg's 

 Foundry at Islenburg, upon the appearance of liquid and solidifying 

 Cast Iron imder the Microscope. Mr. Schott contended that each 



