732 



SUMMARY OF CUKKENT KESP^AKCHES ItELA-JiNG TU 



Voigtlander and Sons' Screw-micrometer Eye-piece.* — Fig. 117 

 shows this auxiliary in section and end elevation. It is intended for the 

 most exact measurements, and contains a carefully cut screw moving a 



Fig. 117. 



glass scale divided in millimetres. The parts of division on the drum are 

 0*01 mm,, and therefore measurements of O-OOl mm. are obtained. 

 The apparatus is placed in the tube in lieu of the ordinary ocular. 



"^H." — Eye-pieces of the Huyghenian or Negative Type as corrected for Achro- 

 matism and Equal Deviation at the Lenses. 



[Among other things it is shown that in practically constructing a telescope 

 eye-piece, it is necessary to depart widely from Huyghen's formula, the 

 only one discussed in text-books.] 



Eng. Mechanic, Ixxxv. (1907) pp. 567-9 (6 figs.) ; pp. 588-9, 612-13. 



C3) Illuminating' and other Apparatus. 



Simultaneous Projection of Two Different Preparations in the 

 Field of the Microscope.! — F. K. Studnicka's "pancratic" Microscope 

 has been noticed in this Journal,:]: and the author now describes how it 

 may be advantageously employed for simultaneously viewing two 

 different preparations. One of his pancratic methods involved the 

 accurate insertion of a reverse objective in the diaphragm-carrier of the 

 Abbe illuminating apparatus from which the condenser had been 

 removed. On a special stage below the ordinary one, a preparation is 

 placed which comes into focus as a reduced reverse image not far from 

 the plane of the ordinary stage, and can be observed in the usual manner. 

 If another preparation be now arranged on the upper stage, the two 

 objects can be brought into simultaneous view, the lower object being 

 racked up or down as required. If the sizes of the objects are large, 



* Catalogue (English edition) 1907, p. 42. 



t Zeitschr. wiss. Mikrosk., xxiv. (1907) pp. 34-8. 



1 See this Journal, 1905, p. 643, 



