Hall, 07i a New Form of Condetiser. 



109 



Mr. Swift has in hand a new and cheaper form of parabo- 

 loid, that will be made to fit and work in the meehanical 

 arrangements of this instrument ; it will eventually make 



A. Optical combination. 



B. Rack adjustment for focussing, 

 c. Sliding frame with black spots, 



for dark-ground illuminatiou. 



D. Large diaphragm. 



E. Rotating cap to carry test stops, 

 f . Small diaphragm of apertures. 

 G. Polarizing prism. 

 H. Selenite diaphragm. 

 I. Oblique light shutter. • 



part of the condenser I shall have to mention presently. 



The mechanical portions of the condenser consist in the 

 cheap form of an outer tube having a bayonet catch to attach 



VOL. XVI. k 



