368 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



hand motion. The coarse adjustment is by rack and pinion ; the fine- 

 by micrometer screw. The Microscope is fitted with the Abbe illuminating- 

 apparatus, hollow and plane mirrors. 



Tafner's New Preparation Stand.* — This is made by G. Reichert,. 

 and is shown in fig. 61, about one-third full size. The arrangement 

 will be easily understood from the illustration. 



Fig. 61. 



Imperial Standard Yard.f — A description of the Comparator, and 

 the method of using it, would be outside the range of our work, but we 

 may legitimately examine the micrometer Microscopes by which the 

 measurements are made. These seem to be of a most elementary type, 

 and as such wholly inadequate for the work in hand. The N.A. of the 

 objectives is something under * 1, their greatest separating power is there- 

 fore less than '0001, so that tottoo m - must be taken as the limit of the 

 accuracy of this comparator. All refinements, such as an error of '01° C. 

 in a thermometer, or the compression of the rod due to a change in the 

 barometric pressure, are meaningless when such elementary microscopical 

 micrometers are employed. Apparently the whole of the apparatus was 

 made abroad. 



(2) Eye-pieces and Objectives. 



Reichert's New Erect Image Preparation System for Preparation 

 Microscopes.^ — This system of lenses, as applied to Reichert's Large 

 Model Preparation Microscope, is shown in fig. G2. The arrangement 

 of Porro prisms by which an erect image is obtained is seen in section. 



* C. Reichert (Vienna), Catalogue No. 25 (Mikroskopie, 1904) p. 41, fig. 20a. 

 f Memorandum on the Construction and Verification of a new copy of thf- 

 Imperial Standard Yard. Part I. London, 1905, 57 pp., 4 pis. 



X C. Reichert (Vienna) Catalogue No. 25 (Mikroskopie, 1904) p. 40, fig. 20. 



