ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 99 



old form of substage construction, preferring to modify other arrange- 

 ments to adapt them to this construction rather than change their model. 

 In England the mechanically movable iris-diaphragm was not adopted 

 by English makers. The simpler method of the shallow carrier above 

 the iris-diaphragm into which stops for dark-ground illumination, for 

 oblique illumination, or various stops for experimental purposes could 

 be dropped, was found to render all the service necessary. Those, says 

 Rheinberg, who have worked with both forms will be in little doubt 

 as to which is the more convenient. 



The correspondence is continued by J. E. Barnard,* who admits that 

 the characteristics of the English and German models are, on the whole, 

 fairly set forth, but that the section on comparison of the two types is so 

 prejudicially drawn as to amount to little more than a eulogy of the pro- 

 ductions of Continental houses, and that, if the concluding sentences 

 were to be accepted, the English producers would have no alternative but 

 to abandon the field and leave their Continental rivals in possession. Id 

 Barnard's opinion the original article was written from the point of view 

 of the producer, the value of the user's experience being ignored. Hence 

 it is that the criticisms on the substage arrangements are so unconvinc- 

 ing. In most Continental types these are far too cramped, and the 

 absence of a fine-adjustment, so far from being an evidence of superior 

 workmanship, merely testifies that it is unnecessary. An achromatic 

 condenser, even of the finest optical construction, does not focus within 

 such narrow Ihuits that a fine-adjustment is required. A well-made 

 rack-work will, in fact, give a sufficient degree of accuracy. He has 

 no doubt as to the superiority of the tripod- in comparison with the 

 horseshoe-foot. For photomicrograghy no well-designed stand should 

 require clamping to its base at all, and the best of Continental Micro- 

 scopes, even those specially designed for the purpose, are so unstable that 

 they will not stand alone when horizontal, much less retain any degree of 

 stability in that position. He points out that the statement that the 

 larger stands of English makers require clamping-down is not in accord- 

 ance with the facts, as he has recently had a Microscope made by a lead- 

 ing English manufacturer which was more stable in the horizontal than 

 in the vertical position. He cites his own practical experience in support 

 of his views. 



The assertion in the original article that the Continental model is an 

 evolution from an exceedingly simple and, by inference, highly satis- 

 factory design, is sternly challenged. So far from this being really the 

 case, the refinements on the model Continental stand have been almost 

 entirely borrowed or copied from more perfect English models. As 

 regards the alleged complexity of a high-class English Microscope, it has 

 yet to be shown that the adjustment cannot be made in as many minutes 

 as the writer would apparently postulate hours. 



As regards the alleged superiority of the centration of the objective, 

 as in the Continental instrument, over the centration of the substage 

 condenser, the writer overlooks the facts (1) that the optician makes the 

 eye-piece and objective as coaxial as possible ; (2) that the condenser is 

 an independent optical system, on a separate part of the instrument ; 



* Nature, No. 2204 (1912) pp. 412-13. 



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