362 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fig. 72 gives a section through the apparatus. Over the : grating J 

 an obliquely-set small glass plate with parallel plane sides is placed, 

 serving both for protection of the grating as well as for the reflection of 

 the scale image. The screw E operates against the spring L, and F 

 against the spring N. M is the rotatory wave-length scale, which E'the 

 sleeve P pushes into the front focal plane of the projection ocular. > The 

 lens Q acts as the collective glass of a Huyghens ocular. The achro- 

 matic collimator objective has a free diameter of 11 mm. and a focal 



..■■■■ 



Fig. 74. 



length of 50 mm. The telescope objective S is similar. The telescope 

 ocular T magnifies about 15 times the real diffraction spectrum trans- 

 mitted through the telescope objective S. 



Fig. 73 shows the entire apparatus ready for use as applied to 

 Zeiss' No. l c stand. 



Koenigsberger's Microphotometer for the Measurement of Light- 

 Absorption.* — In the construction of this instrument J. Koenigsberger 



* Zeitschr. f. Instrumentenk.. xxi. (1901) pp. 129-33 (2 figs,). 



