98 SUMMARY OF CUKKENT UESEA.11C11ES UKLATING TO 



and the Continental models as now existing, and they deal with the 

 changes in process of evolution. The points, some nine in number, 

 which go to constitute an " English " Microscope are carefully sum- 

 marized, and admittedly render it an instrument of great precision. 

 But it is argued that this very excellence renders such a Microscope too 

 elaborate for an average worker, and that the simpler types evolved — 

 too slowly, unfortunately, for the demand — compare unfavourably with 

 the " Continental " type, which, having no past to speak of, was able to 

 adapt itself the more readily to the wants of those who did not care so 

 much how they saw so long as they could see. The writer considers that 

 the old terms " English " and " Continental " will soon cease to have any 

 real meaning, and are certainly not significant of the place of origin. 



The two types, starting from opposite poles, have lately reached 

 common ground as regards the majority of the instruments produced, 

 and there is little to choose between them for mere demonstration of 

 known structure. But to get the finest results out of any optical 

 system, centration along the axis, and, in the case of a microscopical 

 system, interchangeability of parts, not only above but below the stage, 

 is essential ; few Continental Microscopes possess the means of doing this, 

 while every English stand of the first class is so provided. Therefore, 

 considers the writer, the conclusion of any unbiassed observer must be 

 that the English type is the better in the hands of the expert, who wishes 

 not merely to demonstrate the known but to reach out, maybe, into the 

 unknown ; but what is best for the master of his instrument and sub- 

 ject is not always good for the average man, and there are minor details, 

 such as the method of fixing the mirror, etc., in the Continental pattern 

 which make it easier of use by those who merely look on the Microscope 

 as a tool ; and this, combined with the greater handiness in the vertical 

 position when wet preparations are under examination, makes the Conti- 

 nental type more acceptable to the laboratory worker. The writer, how- 

 ever, points out, as redundances in the Continental model, the circular 

 rotating stage and the excentric rotating movement of the iris-diaphragm 

 below the Abbe condenser. The former can only be useful in petrology, 

 and the latter renders no service to direct illumination. But the mode 

 of fixing the mirror on a swinging tail-piece he considers a positive dis- 

 advantage. This mode of fixing the mirror is found also in practically 

 all patterns of the English type, and it is, in the writer's opinion, the 

 combination of the altogether undesirable swing tail-piece with the 

 desirable (if understood) centring substage that has caused the prejudice 

 (for such it amounts to) in certain quarters against the English type. 



In a letter to the editor of Nature,* J. Bheinberg points out that in 

 England substage illuminators were in general use long before this was 

 the case on the Continent. They were originally intended, as their name 

 implies, for concentrating light on the object. But the Abbe substage 

 was primarily only designed by its originator for the testing of objectives 

 and for experiments on the effects of diffraction ; it was at first only 

 chromatic and used for narrow cones of light. Although the utility of 

 achromatic condensers and wide illuminating cones is now generally 

 recognized on the Continent, most Continental makers still cling to the 



* Nature, No. 2202 (Jan. 11, 1912) p. 348, 



