420 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



(2) Eye-piea||s and Objectives. 



New Achromatic Objectives.*— In the most recent catalogue of the 

 firm of Carl Zeiss there are listed two new oil- immersion y^^ lenses. 

 One is an ordinary achromatic, with N.A. of 1*25; the other is a 

 fluorite achromatic, the X.A. being 1*30. The equivalent focus of both 

 is 1*8 mm. 



(3) Illuminating- and other Apparatus. 



Recent Developments in Drawing by the aid of Projection Appa- 

 ratus used on the House-lighting System.f — S. H. Gage describes the 



Fig. 57. 



chief latest forms of projection apparatus, and gives a large number of 

 practical suggestions. His paper is copiously illustrated, and includes 

 the following plates, which may perhaps be useful to readers of this 

 Journal. 



Fig. 57 shows the author's apparatus for drawing with the Microscope 

 and a movable table with large plate-glass mirror, a-a-a is the axial ray 

 of the illuminating and image-forming beam ; h, base-board of the optical 



* Carl Zeiss Catalogue, 1913, p. 21. 



t Trans. Amer. Micr. Soc, xxxi. (1912) pp. 177-97 (16 figs.). 



