Boyal Microscopical Society. 51 



concentric rings, after which the radii became spirally twisted and 

 plumose, and terminated in straight lines, regaining, their normal 

 direction. Several of the gyrating portions had the appearance of 

 spirally twisting about their own axes. This aspect probably 

 resulted merely from the arrangement of colour, light, and shade 

 obtained by the action of polarized light. 



In other cases feather and landscape effects were obtained, 

 owing a good deal of their richness and diversification to the silica 

 cracks and changes of level. 



By dissolving salicine in the solution of colloid silica — aiding the 

 operation hj heat — something Hke the pavement pattern of the 

 copper slides was occasionally obtained, each compartment being 

 filled with a beautiful group of crystals assuming the shape of a 

 pink, or some such flower. At other times the circular and radial 

 patterns so well known to microscopists were modified by the radii 

 becoming plumose, and more or less curved. In a few instances a 

 very elegant fan-shaped and extremely delicate crystallization sprang 

 from solid crystals like fan-handles, the fan portion being decorated 

 with concentric rings, and terminating in a border of fine needles, 

 looking like a silken fringe, and appearing under suitable illumina- 

 tion to be in a different plane from the fans themselves. 



Hippuric acid similarly treated yielded flower patterns of great 

 beauty, some of them taking the form of what the botanists call a 

 ringent corolla. These are usually of extreme delicacy, and only 

 seen well in one or two positions of the polarizing apparatus.* 



Tartaric acid used in the same way gives irregular pavement 

 patterns, some of the compartments looking fiat, and of more or less 

 uniform tint, while others appear slightly raised and ribbed, bearing 

 some resemblance to coloured acorn-barnacles. The actual varia- 

 tion of level in these cases is very slight ; far less than what the 

 perspective action of shade and colour would make it aj^pear. 



All these crystals require careful management of the polarizing 

 apparatus, and a selenite stage to bring out their full beauty. The 

 "neutral tint stage" of Mr. Ackland shows them extremely well. 

 When properly displayed it will be found that cr} stals prepared in 

 this way afford a greater range of colour than is common, and the 

 artistic defect arising from too violent contrasts is avoided. The 

 observer should not be satisfied unless the primary tints are asso- 

 ciated with a sufficient variety and quantity of secondary and ter- 

 tiary tints to produce a true chromatic harmony. 



It is impossible to view a number of slides prepared in this way 

 without being struck with the resemblance of many of the patterns 

 to those of sections of various structures in organized beings, and we 



* Quite different patterns were obtained on other occasions. The author hopes 

 shortly to bring before the Society, and publish in this Journal, illustrations of 

 some of the most remarkable forms obtained with different bodies. 



