232 SUMMARY OF CURREN.T RESEARCHES RELATING TO 



of the lowest powers, will not satisfy the chemist. For the use of bota- 

 nists, zoologists and bacteriologists there is a certain similarity of require- 

 ments, but even here it would be unwise to endeavour to make all 

 Microscopes on one model. The work of the student in the botanical 

 laboratory is totally different from that of the research worker who is 

 making photomicrographs with the highest power immersion lenses. 

 Beck deals with many points in detail, and on the question of the form 

 of a Microscope he considers that its stability does not depend upon 

 whether the base is of the tripod or of the so-called horseshoe pattern. 

 It is universally admitted that it should stand on three points, and the 

 test of stability that should be applied is, at what angle will it upset, 

 and what force is required to make it do so ? 



J. "W. Ogilvy, * as the writer of the third section of the original 

 article, replies to Barnard's and Sutchffe's criticisms, and defends his 

 own views. 



F.R.M.S.f advocates the superiority of sub-stage centring over nose- 

 piece centring, and is in favour of the mechanical draw-tube. As regards 

 the standardization of sub-stage fittings he points out that difficulties 

 naturally arise if the Royal Microscopical Society's gauges are not 

 adhered to. While English makers loyally work to those gauges, Con- 

 tinental makers each have two or three different ones. The writer dwells 

 on the necessity for systematic teaching in the elementary technique of 

 the instrument. It is not unusual to meet men of eminence who are 

 constantly working with Microscopes, and who do not even know that a 

 sub-stage condenser requires to be focused. How is it possible that the 

 refinements of the English Microscope can appeal to their students ? 



F. E. Brand :j: writes from the point of view of one who has had 

 practical experience in both English and Continental factories in the 

 actual manufacture and testing of Microscopes. He thinks that the 

 recent extension of the rear toe in the horseshoe stand has given it a 

 stability equal to that of the tripod form. No matter which stand 

 is used in photomicrography, clamping is essential. The attachable 

 mechanical stage is intended for certain classes of work only, and should 

 not be used if found inconvenient. The necessity of a centring device 

 to a substage condenser, in preference to the fixed form, is a matter for 

 the individual worker to determine. AVith regard to the standardization 

 of substage fittings. Brand points out that it is a mechanical impossi- 

 bility to make smooth sliding fittings interchangeable where tubes are 

 employed, one of which is sprung in order to maintain a certain constant 

 tension, unless a pressure-screw is used, which arrangement could, 

 however, only be used with a centring appliance. The standardization 

 of objectives is a totally different matter, as greater latitude is per- 

 missible in cutting the threads, the tension being obtained on the 

 shoulder of the objective mount— i.e. when the objective is screwed 

 right home. 



In respect to sprung slide-fittings versus ground-in slide bearings, 

 Brand sums up in favour of the latter, especially as adopted on the best 

 Continental Microscopes. He also points out that objectives provided 



* Nature, No. 2206 (1912) p. 481. 

 t Nature, No. 2207 (1912) p. 515. 

 X Nature, No. 2208 (1912) p. 349. 



