Boyal Microscopical Society. 239 



bubbles. A little gentle violence will displace some of the bacteria 

 and fungoid-like bead groups. Fig. 6 group shows a spurious fungoid 

 portion, only partially resolved into beads ; another portion perfectly 

 resolved. Figs. 7 and 8, remarkable forms seen with jV^h. 



I am indebted for the beautiful drawings of these objects illus- 

 trating this paper to Dr. Anthony, whose skill both as an observer 

 and artist is well known to and highly appreciated by his brother 

 Fellows of this Society. 



The size of the silica spherules forming the films varies, but less 

 so than might at first be supposed, as only those that are favourably 

 situated and carefully illuminated can be distinctly resolved and 

 separated from their neighbours. In two slides Dr. Anthony found 

 most to be about ^TroirTr" in diameter, and some close upon TTrtrVTSTy'. 

 In a shde sent to Dr. Pigott, he found them to vary from between 

 4 W to TTrirVo-^", and " had no doubt many by proper illumination 

 can be seen much less than this." The real size of the beads pro- 

 bably varies according to the rate at which the gas is evolved and 

 decomposed by contact with the glycerine and water, and it is the 



writer's opinion that the smallest beads are considerably less than 

 1 " 



TOUOOTT • 



By gently rubbing the films with water in a small agate mortar, 

 avoiding any force likely to pulverize the surface of the mortar itself, 

 they may be separated into myriads of beads, and these with a little 

 washing and subsiding on a slide, may be obtained in nebulous 

 clouds, or more widely scattered. Multitudes of beads in this con- 

 dition appear excessively minute, and so do those in the thinnest 

 and most transparent films. If such beads are examined with a 

 series of fine objectives, the observer will consider them smaller 

 pretty nearly as it is the theoretical duty of his objective to make 

 them bigger. Thus operating with ^th of Beck, ^th of Powell and 

 Lealand (estimated somewhat too low), and ^V^h of Nobert (esti- 

 mated too high), the beads were far from increasing in proportionate 

 apparent size as the magnification passed from between 200 and 300 

 to between 2000 and 3000, according to the objectives and eye- 

 pieces employed, and the strongest conviction of their real minute- 

 ness was obtained with the highest power. No glass can give the 

 real size of minute highly-refractive lenses, but experiments with 

 these beads led to the belief that with glasses of fine construction 

 those of the highest power have least proportionate error, contrary 

 to what might have been supposed, and yet quite in accordance with 

 the experience of those who employ objectives up to ^^th for very 

 minute researches, instead of relying upon a dictum once current 

 that iV of extreme aperture would suffice for any magnification 

 required. 



These results appear to be in accordance with calculations made 

 by Mr. Lister, showing that certain proportions ought to exist 



T 2 



