T'O- 



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Obtaining Monochromatic Light, By E. J. Spitta. IT 



saves the operator frequently 

 jumping up and down from his 

 seat ; and secondly, it prevents 

 his eye being thrust often and 

 suddenly into the bright light of 

 the incandescent lime, which is 

 quite sufficient to dull its per- 

 ceptive faculties for some little 

 time. A black glass window, 

 however, is let into the case 

 covering the jet, through which, 

 if necessary, the lime can be 

 viewed without inconvenience. 

 The light from the lime is caught 

 by a 6-in. compound condenser, 

 which, after passing through one 

 of Zeiss' thick water-baths, is 

 focussed on a slit, the size of 

 which is not of much import- 

 ance, the one in use being 

 about 17 mm. long and 4 wide. 

 Focussed upon the other side of 

 the slit is a lantern-lens of 5-in. 

 focus, thus forming a collimator 

 from which issue parallel rays 

 upon the film mounted on its 

 corrective prism. This prism is 

 mounted on a table which re- 

 volves on its vertical axis, gra- 

 duations of a coarse description 

 being added for convenience. 

 All these details are mounted 



on Zeiss' saddles to slide on the 



optical bench, and when the 



suitable position is found for 



each of them they can be locked 



at will. From the prism the 



rays fall upon the substage 



condenser of the Microscope, 



the instrument being bent at 



right angles so as to stand on 



the little table fixed to the base- /" 



board upon which everything 



rests. Everything save the *» 



Microscope is covered in by a 



suitable casing, which can be 



easily opened if required, dia- 



!*■ 



Feb. 18 th, 1903 



