560 



SUMMARY OF CURKENT RESEARCHES RELATING TO 



(3) Illuminating- and other Apparatus. 



Apparatus for Drawing in Natural Size, or with Slight Mag- 

 nification or Diminution.* — This apparatus (^tig. 99) is made by Messrs. 

 Leitz, and is described by C. Metz. It is due to some suggestions made 

 by Messrs. Brocher and Doret in the Revue Medicale de la Suisse 

 Romande.f The apparatus will be easily understood by the figure. It 

 resembles an Abbe drawing apparatus, but an isosceles right-angled prism 

 is substituted for the rhomb, and its hypotenuse plane is silvered. A 

 mirror 8 cm. by 10 cm. pushed to the end of a guide rod, attached by a 

 jointed arrangement to a heavy foot, is kept at an angle of 45° by means 

 of a notch. The prism leaves half of the opening free. Above this 

 would be the observer's eye, and the plane A would be seen direct. The 



plane B is seen by rays reflected at mirror and silvered surface. It is 

 subdued by means of smoked glasses which are inserted on the mirror 

 side in front of the prism : two such glasses of equal intensity are pro- 

 vided ; they therefore give two degrees of brightness. For subduing the 

 plane A three glasses are provided. The drawing apparatus is placed on 

 the stand in such a way that it is at the distance of natural vision from 

 the table. Adjustment is made by rack-and-pinion. The ajDparatus is 

 fitted with four bi-convex lenses, and is capable of producing two-, three-, 

 four-, or five-fold magnification. If enlargement is desired, the object is 

 placed on the plane A under the lens, and the plane B becomes the 



* Zeitschr. wiss. Mikrosk., xxix. (1912) pp. 79-81 (1 fig.), 

 t See this Journal, April 1912, p. 244. 



