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SUMMARY OF CURRENT RESEARCHES RELATING TO 



will give an extended conjugate focus to the object-glass, so as to 

 convert the combination into a kind of telescope. 



The apparatus (figs. 135 and 136) consists of a pair of plano- 

 convex lenses mounted in a tube fitting in an adapter which is placed 



Fig. 135. 



Fig. 136. 



over the eye-lens of an ordinary eye-piece when the eye-guard is 

 removed. A pin-hole diaphragm is fitted over the upper lens, and 

 the combined focus of the two is about ^ in. To allow of adjustment 

 for focus the lenses slide in the adapter, and when adjusted the eye- 

 point (or " Eamsden " circle) can be focused and viewed through 

 them. 



The centering glass is used in conjunction with a cap, having a 

 pin-hole aperture, fitting over the illuminator, so that the collimation 

 of the two pin-hole diaphragms with the source of light will afford a 

 ready method of adjusting the illumination exactly in the optic axis. 



In practice, the pin-hole cap is first applied over the illuminator, 

 and the image of the source of light seen through it is centered 

 approximately with the ordinary eye-piece ; the centering glass is 

 then put over the eye-piece, and the exact collimation is obtained by 

 the adjustment of the centering-screws of the substage, and by slight 

 movements of the mirror or source of light. 



Amici Polarizing Apparatus. — We recently found in Florence 

 a piece of apparatus belonging to an Amici Microscope, the construc- 

 tion of which was somewhat puzzling. On submitting it to Mr. 

 H. G. Madan, he reports as follows : — 



" The apparatus (fig. 137) consists of a square brass box containing 

 10 thin plates of glass (the glass has a decided blueish tinge, and is 

 not very perfectly polished). On the top of the plates lies a right- 

 angled prism of glass (refractive index = 1 • 512) ; the hypothenuse 

 of the prism being parallel to, and in contact with, the top plate. 

 The box is supported on a brass stem in such a position that the plane 

 of the glass plates makes an angle of 118° (approximate) with the 

 axis of the Microscope, under the stage of which it is fitted ; and it 



