December 21, 191 1] 



NATURE 



245 



MICROSCOPE STANDS. 



CONSIDERABLE attention is now being directed 

 by those interested in microscopy to various 

 questions connected with the build of the instrument 

 irrespective of the purely optical parts. We have 

 thought it desirable, therefore, to ask the opinions of 

 those with large experience in the designing and 

 production of stands both here and on the Continent. 

 These opinions are given below. 



Claim for Superiority for the English Stand. 



By the term "English microscope" is meant the 

 distinctive type of instrument which has been 

 built to embody conveniences for working with modern 

 high-class objectives and condensers, which conveni- 

 ences cannot be found in combination in any other 

 microscopes than those of British origin. Among 

 them are the following: — (i) *The tripod foot; (2) *a 

 long range of coarse adjustment for the use of low- 

 power objectives ; (3) *the body tube fitted with mechan- 

 ical draw tube to allow for the adjustment of objec- 

 tives for thickness of cover-glass; (4) the mechanical 

 stage scientifically constructed as a part of the whole 

 instrument ; (5) the compound substage with rackwork 

 to focus and screws to render the substage condenser 

 axial with any objective that may be in use ; (6) *fine 

 adjustment to substage; (7) *the Wenham binocular 

 body; (8) the various fittings for substage apparatus, 

 eyepieces, and objectives of the Royal Microscopical 

 Society's standard gauge; (9) *all the working parts 

 fitted with sprung bearings and controlling screws so 

 that compensation for wear and tear may be readily 

 effected. 



In the English microscope alone are all these con- 

 veniences to be found in combination. In isolated 

 instances one or two of the fittings are included in 

 microscopes of foreign origin, but none are provided 

 w'ith those marked with an asterisk, in the manner 

 that is usual in the English instrument. 



Numerous microscopes are made in Great Britain 

 which are not of the typical English model, designed 

 for students and special uses, but even in these it is 

 customary to incorporate some of the qualities and 

 conveniences enumerated above, and they permit of 

 greater latitude in individual working on the part of 

 the intelligent user than is possible with a microscope 

 which must of necessity be used as a tool that mag- 

 nifies on account of its limitations. 



The English microscope has never suffered from 

 want of appreciation on the part of those who have 

 had leisure or taken sufficient interest to use its many 

 refinements, and it is significant that it is the prevail- 

 ing type that is employed by the thousands of amateur 

 workers throughout the world to-day. 



To the professional worker it has not appealed in 

 the same degree, but gradually he is appreciating the 

 fact that to do the best he must have the many facili- 

 ties that the English microscope affords, and it is in 

 consequence gradually displacing instruments of 

 |impler construction. 



The English microscope has always been of sub- 

 tantial proportions, but a definite advance in its pre- 

 jclsion took place when between twenty and thirty 

 years ago it was recognised by the leading exponents 

 jof microscopy, and especially Dr. Dallinger and Mr. 

 ;E. M. Nelson, that the improved optical means then 

 introduced could not be advantageously employed with- 

 out adequate mechanical conveniences. A slower act- 

 in i,"^ fine adjustment suitable to the increased numerical 

 ipfTture of objectives was the earliest step, and after 

 niany years' insistence that the now almost extinct 

 -ilin'ct-acting fine adjustment was sufficient for all 

 NO. 2199, VOL. 88] 



requiremenis, the Continental makers fell into line 

 with the English makers. 



Then followed the mechanical draw tube, and only 

 those who have seen the beautiful manipulative effects 

 obtained by leading workers, can realise what can be 

 done by its use in correcting for slightly different 

 thicknesses of cover-glass. It has been stated that 

 a difference of draw-tube length of 5 mm. is of no 

 practical importance, but this is not the experience 

 of the modern worker. His critical effects are obtained 

 within closer limits. 



Improvements were simultaneously introduced into 

 the general design of microscopes, refinements which 

 advanced workers found desirable were incorporated, 

 and British manufacturers produced instruments which 

 are to this day known by the name of the microscopist 

 who provided the specification. 



The result has been that the English microscope is 

 a distinctive one, and is unlike its contemporaries of 

 other countries in several important features. 



The mechanical stage of the English microscope, 

 built as part of the instrument, has very forcibly re- 

 vealed its advantages in connection with the recent 

 introduction of immersion paraboloids and reflecting 

 condensers. The attachable mechanical stage of the 

 Continent carries the object slip along the surface of 

 the stage. For these immersion paraboloids it is 

 essential that the under-side of the object slip shall be 

 in contact, by means of immersion oil, with the top 

 lens of the paraboloid. It will be obvious that as the 

 mechanical screws carry the object slip along the sur- 

 face of the stage the oil from the under-side of the 

 object slip will pass on to the stage surface. The 

 immersion oil is thus drawn away and the contact is 

 no longer maintained. The same effect is produced 

 with any immersion condenser, so that in effect the 

 attachable form of mechanical stage largely interferes 

 with the proper working of any condenser or para- 

 boloid which may be of the immersion type. 



It should be borne in mind in this connection that 

 the Abbe illuminator, if used in its full efficiency, must 

 be immersed. This fact is generally overlooked, and 

 it is exceedingly rare for an Abbe illuminator to have 

 its maximum numerical aperture developed by means 

 of oil immersion. 



The English mechanical stage has each plate work- 

 ing independently, and the object is carried in a fixed 

 position on the top moving plate. The oil therefore 

 does not run on to the stage surface as in the pattern 

 just mentioned. 



The compound substage is typically English. The 

 necessity for centring screws to enable the optical 

 centre of the substage condenser to be adjusted to the 

 objectives in use has to this day not been recognised 

 by Continental opticians. 



" A fine adjustment to the substage was the accom- 

 paniment to the more general use of the oil-immersion 

 condenser, the absolute focussing that this required 

 being realised better by this means than by coarse 

 adjustment only. 



There is still want of conformity with the Royal 

 Microscopical Society's substage size on the part of 

 non-British makers, and the condensers are not inter- 

 changeable without alteration. 



The advantages associated with the tripod foot 

 which, properly proportioned, is light in weight, and 

 yet imparts rigidity which is not possessed by any 

 other shape, the convenience of being able to use low- 

 power objectives, and the Wenham 's binocular body 

 with its exquisite stereoscopic effects, and, finally, the 

 obviously better construction from a mechanical point 

 of view of fittings that are adjustable in consequence 

 of wear, all unite to make the British microscope an 

 instrument of precision. 



