326 



SUMMARY OF CUREENT RESEARCHES RELATING TO 



of that by Dr. Benecke (p. 143). It not only allows the angles of 

 inclination of the slide to be varied to a definite extent and accurately 

 measured, but it also enables the observer to bring the axis of 

 inclination into exact agreement with the optic axis, a point which 

 Dr. Fritsch considers to be of the greatest importance, as otherwise 

 the two pictures will not be " stereo-identical." Fig. 63 is a side view, 

 and fig. 64 a view of the apparatus from below. The base-plate con- 

 sists of an outer frame a a, with an inner plate attached to the stage 

 by two pins b h. The frame is movable laterally on the plate by the 

 action of the screws // worMng against the sides of the stage. ^ 



The inclining plate is at c c, and it can be set at different 

 inclinations (on the axis x) by the screw e acting against the springs 



Fig. 63. 



Fig. 64. 



n n. The slide is not placed on this plate, but on a second plate d, 

 which lies over the former, and which can he inclined (by the screw 

 g), on an axis at y. The object of the second plate is to compensate 

 for the thickness of the slide. At ^ A is a graduated arc for record- 

 ing the inclination, and at m m spring clips. 



The centering of the apparatus is effected by using a spider line 

 stretched in the optic axis and a slide ruled with parallel lines. On 

 tilting the plate c first to one side and then the other, any defects in 

 the centering can be readily noticed, for if properly centred no 

 alteration of the focus will be required for the centre ruled line, which 

 will remain in focus at ail inclinations of the plate.* 



Kellicott's Moist Chamber, t— Professor D. S. Kellicott suggests 

 a modification of Dallinger and Drysdale's moist chamber, which 

 he thinks is an improvement. Instead of cementing the thin glass 



* Festschr. zur Feier d. hundertjahrigen Bestehens d. Gesell. Naturf. Freunde 

 zu Berlin, 1873, pp. 75-95 (6 figs, and 6 stereophotographs). Cf. Stem's ' Das 

 Licht,' 1884, pp. 201-3 (2 figs.). 



t Amer. Mon. Micr. Journ., vii. (1886) pp. 267. 



