396 



SUMMAEY OF CURRENT RESEARCHES RELATING TO 



plant, and the connection of its production and destruction with the 

 intensity of the light, have been already fully described,* and we 

 now add Dr. A. Tschirch's description "j" of the special Microscope 

 which Professor Pringsheim constructed for observing the effect of 

 a high intensity of light on objects directly on the stage, and to 

 carry out his method of " microscojiical photo-chemistry " — a method 



which he considered would also 

 be valuable in investigating 

 the action of light on proto- 

 plasm and the formed consti- 

 tuents of the cell-body, for 

 investigations on the sensations 

 of heat in the lowest animals, 

 and in certain cases for ascer- 

 taining the truth respecting 

 the presence and seat of the 

 perception of light. 



The instrument is three 

 times larger than the ordinary 

 [German] Microscopes, and its 

 form resembles that of the 

 older Schieck stand. Upon a 

 firm tripod a rests the conical 

 column b, to which is fixed the 

 large round mirror s. The 

 latter is 160 mm. in diameter, 

 and is as strictly plane as 

 possible. It receives the sun- 

 light from a heliostat, whose 

 mirror must be considerably 

 larger than that generally 

 used, so that the mirror of 

 the Microscojje may be fully 

 illuminated at any altitude of 

 the sun ; 235 mm. by 165 mm. 

 is a sufficient size. At a dis- 

 tance of 165 mm. above the 

 mirror, the column supports a 

 large stage c, about 110 mm. 

 square, beneath which the lens- 

 system is screwed for the pro- 

 duction of the sun's image. 

 In the instruments hitherto 

 employed, a doublet of two 

 plano-convex lenses is made use of, placed in the same frame I, 28 mm. 

 from each other. The lower has an aperture of 66 mm. and a focus 

 of 93 mm., the aperture of the upper being 48-4 mm. and the focus 

 35 mm. In this position they form a round image of the sun • 35 mm. 



* See this Journal, iii. (1880) pp. 117-19. 323-4. 



t Zeitschr. f. Instrumeutenk., i. (1881) pp. 330-3 (4 figs). 



