130 THE AMERICAN MONTHLY [Apiii 



Such an illumination was felt to be a desideratum in 

 quite early microscopical days, and in all the older text- 

 books will be found descriptions of apparatus to serve 

 this end, rang-ing- from simple contrivances like waxed 

 paper, ground glass and plaster-of-Paris mirrors to light 

 modifiers, reflector screens, white-cloud condensers, 

 double parabolic specula, and many more elaborate de- 

 vices. It is pretty obvious, therefore, that nothing- new or 

 striking- is likely to be invented for the purpose now, 

 when the tendency is to diminish rather than multiply 

 apparatus. 



The idea is to intensify the light and then spread it over 

 a larg-e surface. For the intensification I use the lower, 

 crossed lens of the Abbe condenser, {fig. 2, b) but any 

 suitable fairly large lens of about one inch focus will do as 

 well, either a double convex or the field lens of an eye-piece. 

 This is screwed into the lower end of a piece of tube 

 fitting the sub-stag-e, or under stage ring-, which tube 

 should be a little long-er than the focal leng-th of the lens 

 employed. Just below the upper end of the tube is a split 

 ring- serving- as a ledg-e, and on this, in the focal plane of 

 the -lens, rests a circle of thinnish g-lass lightly g-round 

 on one surface. The lig-ht from the flat of the lamp is 

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

 throug-h the lens and focussed on the g-round glass, (fig-. 2, a) 

 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 g-round g-lass, with a little 

 manipulation one can fill any sized field with a most 

 pleasant soft lig-ht, which can be employed for a long time 

 without detriment to vision. It was long- ag-o discovered, 

 that freshly-g-round g-lass possessed a peculiar property of 

 soft brilliancy which the commercial product did not, and 

 I g-et circles of the required size from the g-lass-cutter and 

 grind them myself with a little fine emery and water on 

 another piece of g-lass until just sufficiently abraded to 

 stop any direct pencils. Besides the ordinary white glass 

 it is a great advantag-e to g-et .some circles cut from dif- 

 ferent tints of blue or smoked g-lass, and either g-rind these 



