250 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



stage. It has been thought best not to provide this apparatus with a 

 contrivance for the projection of diapositives, as the convenience of the 

 hand-movements would irretrievably suffer. 



Diapositive projection, as well as the projection of physical experi- 

 ments, is performed by Schmidt and Haensch's apparatus shown in 

 fig. 56. A lever h x can insert a reflecting glass plate s l5 inclined at 

 45°, for receiving the light-rays coming from the source on the left. 



Fig. 56. 



In consequence, most of this light is reflected downwards at s v and by 

 means of mirrors s 3 , s 4 , impinges on the under side of the object placed 

 on the stage at T. Some of the light, however, passes through s l5 and 

 therefore illuminates the upper surface of the object at T. The effect 

 is to bring out structural and inner details so that a much improved 

 image, by help of the objective and mirror S x , is projected on the 

 screen. If desired, a mirror may take the place of s lt and the object 

 would now be entirely illuminated from below. Or, again, the rays 

 may fall directly on s lf thus giving upper illumination only. 



