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XIX. — On a ParahoUzed Gas Slide. 

 By James Edmunds, M.D., M.K.C.P. Lond., F.K.M.S. 



dBead 9th June, 1880.) 



This is a simple and inexpensive contrivance which has been made 

 for me by ]\Iessrs. Beck for the purpose of examining bacteria, 

 blood-globules, &c., while gases or vapours of various kinds are 

 projected into an annular space from which they rapidly diffuse 

 into an object which is being observed under the Microscope. 



The slide * (Figs. 52 and 53) is constructed of a shp of optical 

 crown glass 3 inches by l^, and in thickness from three to four 

 sixteenths of an inch. An annular zone eleven- sixteenths of an 



Fig. 52. 



inch in diameter and nearly one-eighth inch deep is turned out 

 of the slide, so as to leave a central pillar three-eighths of an inch 

 across, and the top of this pillar is then turned down, so as to 



Fig. 53. 





leave a . li 1 area nearly a quarter of an inch in diameter, and 

 exactly on a level with the general surface of the slide. The out- 

 side of the central pillar is then smoothed into an approximately 

 paraboloidal surface, and brought to an optical polish. A straight 

 groove of the same size and depth as the annular zone is then cut 

 out of the slide parallel to its long side and at a tangent to the 

 annulus. Into the longitudinal groove of the slide two fine glass 

 tubes are cemented. One of these is left projecting beyond the end 



* Fi". 52 sliowH flie iippor (isj^cpt f>f <he sliilo oxeiivatod willi the ;;roovo 

 and iiimuluH, tlio totally n llcctiii;^ iiumlioliziMl «rirfiico of thr cciitnil i>il!ar. aii«l 

 the dtftr central area left on a level with the top of the sliile. Vv^. 5;{ ;,'ive.s :i 

 longitudinal ROction of the slide drawn through its centre, and nhowin>^ the 

 annular gas uhaunel, the central paraboloid, and the thiu cover. 



