254 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



from outside to get the most favourable light-point in this way for any 

 description of projection, whether microscopic or for demonstration of 

 blood circulation in the living frog. The optical bench is placed above 

 the light condenser, so that the space between the condenser and the 

 draw-out shelf remains free and can be made use of. The frame is for 

 slides of 12 by 16 cm. There are a number of accessories, such as an epi- 

 scope for projection of opaque objects with oblique light, a frog-table, &c. 



Beck's New Wide-Angle Oil-Immersion Condenser. — Messrs. E. 

 and .1. Beck, encouraged by the success of their dry achromatic con- 

 denser, have brought out the above (fig. 58), which, 

 although manufactured on a different formula, has equal 

 advantages as to correction. The aperture is 1-4 N.A., 

 which is the full maximum obtainable without the use 

 of special slides and media. It possesses an aplanatic 

 cone, that is to say, the whole of the light in that cone 

 is brought accurately to one point. The optical com- 

 bination consists, as will be seen from fig. 58, of four 

 systems of lenses, and is constructed on a new principle. 

 The front lens may be removed when the condenser is to be used for 

 low-power work. The working distance is sufficient for so large an 



Fig. 58. 



Fig. 59. 



angular aperture, being about 0*06 of an inch. Messrs. Beck strongly 

 recommend this condenser, in conjunction with their latest 1/12 1 "4 N.A. 

 objective, for work requiring critical resolution, and for all hranches of 

 photomicrography. 



Leitz' Bull's-Eye Condenser. — This illuminating lens on a new form 

 of stand is shown in fig. 59, and will be clearly understood therefrom. 



