258 THE HISTOEY AND DEVELOPMENT OF THE MICROSCOPE 



now Ross, adopting this foot, employ the added mechanism of the 

 revolution of the pillar on the foot (an old device) to secure stability 

 at all inclinations (vide fig. 185, p. 232). Surely if the horseshoe 

 foot were satisfactory for the inclining microscope these modifications 

 would not have been deemed needful. Besides which we note that 

 for the same purpose the C mtiiiental maker, whom we venture to 

 think very alert to the true needs of modern microscopy, Reichert, 

 prolongs the projecting 'toe' of the horseshoe, giving it almost a 

 tripod form. 



It must not be forgotten that this want of balance is with the 

 short, not the long body. 



The diameter of the tube is small, being slightly over seven- 

 eighths of an inch. No doubt a low-power eye-piece with a large 

 field is extremely useful as a finder, but this advantage is completely 

 lost with the original small Continental tube. That this is seen to 

 be a disadvantage would appear certain, because the photographic 

 microscope model of Zeiss has a larger body -tube ; and in their recent 

 ' Appendix ' to their latest catalogue they admit that for certain pur- 

 poses other stands made by them, ' owing to the limited diameter 

 of their tubes, cut off the field ; ' a significant fact for those who 

 would narrow the English body, when it is remembered that Powell's 

 is, and has been, suitable for all purposes without alteration, and 

 long, short, and binocular bodies are interchangeable. 



At the date of the publication of our last edition, out of eighteen 

 models ten were made with inclining bodies, and three had sliding 

 coarse adjustment. But in the twelve models for 1889 ten incline, 

 while only two are rigid, and eight have rack-work, against four 

 having sliding tubes for coarse adjustment ; but in the current 

 <?atalogue of Messrs. Zeiss six out of eight models have inclining 

 bodies, two are rigid, and one has sliding coarse adjustment. This 

 is a manifest, if slow, conformity of the primitive model to the 

 English type, and hardly supports the affirmation ' that (during the 

 last forty years) the Continental microscope has closely followed the 

 wants of the microscopist.' 



The direct-acting screw, only slightly modified, obtains universally 

 in these models. We have already plainly said that this is not suf- 

 ficiently delicate in its action for critical work with an apochromatic 

 objective of 1-4 or 1 '5 numerical aperture, especially as a micrometer 

 screw with a necessarily delicate thread is bound to carry the com- 

 bined weight of the body, limb, coarse adjustment, and the 

 opposing spring ; that it will wear loose under the stress of 

 constant work is inevitable, and thus its utility must be wholly 

 gone. 



The 1889 model has a new form of fine adjustment, the alteration 

 being that the micrometer screw acts on a hardened steel point. This 

 may cause it to work smoother ; but as no weight is taken off, there 

 is difficulty in discovering any reason for its admitting of more 

 prolonged use without injurious wear. In support of this is the 

 fact that in the new photographic stand made by this celebrated 

 firm, with so extremely delicate a fine adjustment (fig. 129), we 

 have learned through their English representatives that only one- 



