542 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
L and K. At the front end of the sector, rather close to the axis of 
rotation, is erected the carrier of the collector lens C, consisting of a slab 
20 by 9 cm., perpendicularly fastened to the sector, and pierced at a con- 
venient height by a circular opening in which the collector lens is set ; 
the centre of this opening must be brought by means of the levelling 
screws to coincide with the optical axis of the Microscope used. The 
author employs for his collector the objective of a small opera-glass, of 
12 cm. focus and about 2*5 cm. diameter. In front of the lens a snflall 
bracket, 7 by 9 cm., is applied to the carrier, and on it is placed the carbon 
disulphide prism P, of 60° angle and side-planes 9 by 6 cm. The prism 
is set close up to the collector, so that it is in the position of minimum 
aberration for blue, and is exactly over the rotation axis s. A fillet 1 1 
is screwed on to the bracket, against which the side-plane of the prism 
Fig. 136. 
must lie, in order to avoid the necessity of determining the adjustment 
on every occasion. 
The other carriers must be capable of a sliding adjustment in the 
axis of the apparatus, and for this purpose they are secured, not on the 
sector, but on square foot-blocks of about 9 cm. square. Each of these 
blocks is fitted with three small knobs, so that they may stand steady 
without vibration ; their edges must always be in contact with the 
graduated bar L i. On the first slider is a perpendicular board with an 
adjustable slit, or a revolver frame with several slits, of breadth varying 
between 0*1 and 3 mm. The second slider is similar, but, instead of the 
slit arrangement, carries a n on-achromatic two-lensed system S C, the 
‘ c slit collector,” of about 3*5 cm. aperture and proportionately greater 
focus. The last slider hq is for the light-source, usually a small 
