G. C. KAROP ON ILLUMINATING OBJECTS. 



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the lower end of a piece of tube fitting the sub- stage, or under 

 stage ring, which tube should be a little longer than the focal 

 length of the lens employed. Just below the upper end of the 

 tube is a split ring serving as a ledge, and on this, in the focal 

 plane of the lens, rests a circle of thinnish glass lightly ground 

 on one surface. The light from the flat of the lamp flame is 

 condensed by the bull's-eye on the mirror, thrown up through 

 the lens and focussed on the ground glass, which is racked or 

 pushed up until almost in contact with the slide. The image 

 of the flame being broken up at every possible angle by the 

 ground glass, with a little manipulation one can fill any sized 

 field with a most pleasant soft light, which can be employed 

 for a long time without detriment to vision. It was long ago 

 discovered, I believe by the late Mr. Slack, that freshly-ground 

 glass possessed a peculiar property of soft brilliancy which the 

 commercial product did not, and I get circles of the required size 

 from the glass-cutter and grind them myself with a little fine 

 emery and water on another piece of glass until just sufficiently 

 abraded to stop any direct pencils. Besides the ordinary white 

 glass it is a great advantage to get some circles cut from different 

 tints of blue or smoked glass, and either grind these on one sur- 

 face in the same way, or temporarily cement them to the un- 

 abraded surface of the ground glass, by a drop of cedar oil or 

 glycerine ; one thus obtains a series of tones suited to all sorts 

 of objects. 



a. Ground glass. 



b. Lower crossed lens of condenser. 



