124 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



large scale (natural size) illustrate the construction of the illuminator 

 better than any previously given. 



Figs. 11 and 12 show the illuminator in side view and section 

 as intended for aiii^lication to the large Zeiss stand, Sp being 

 the mirror, z the pin on which the outer diaphragm-carrier r 

 tui'ns, B the inner carrier for the diaphragm disks (b) moved by 

 the milled head g, and T the holder for the optical combination S. 

 The double combination is for use with objectives of aperture not 

 exceeding 1 • 20 N.A., whilst the triple combination has an aperture 

 of 1-40N.A. 



Modification of the Abbe Condenser. — W. Behrcns* modifies the 

 mechanical part of this condenser in the manner shown in fig. 13, to 

 correct principally two inconveniences ; 1st, that the focus of the 

 optical combination cannot be brought much below the object, and 

 2ndly, that the lenses cannot be removed and an ordinary cylinder- 

 diaphragm substituted. 



The bar t has at the lower end the mirror s, and at the upper end 

 the carrier i for the lenses I. The bar is provided with rackwork, and 



Fig. 13. 



is raised or lowered in a vertical direction by a pinion and milled head 

 beneath the stage. The two sets of lenses for use with high and 

 low powers are each attached to a plate which slides (by the milled 



* Zeitschr. f. Wiss. Mikr., 1. (1884) pp. 409-12 (1 fig.). 



