1893.] 



MICROSCOPICAL JOURNAL. 



73 



" Tlic coarsc-jjjraiiiccl, (larU-ci)lort'(l dust wliicli drit'ts, as all 

 Calcutta residents arc aware, into the leeward corners of our 

 flat house-tops is found to contain, mixed with dried portions of 

 orj^anic matter, certain majjnetic and hyaline granules which 

 present appearances hi<;hly indicative of previous fusion. These 

 appear mostlv as opa(|ue oi' translucent spheroiilal bodies, some- 

 times sin<;le and isolated, and sometimes composed of more than 

 one spherule fused together, varving in size from loooth to ^idth 

 of an inch in diameter. The opacpie l)odies vary in color from 

 black to rust\ reil, whilst the transparent spheres, by transmitted 

 light, arc light-brown or vellowish, like colored glass. They 



Explanation of Figures. 



1. Opaque, sliot-like granule. 



2. Spherule including a dark crystalline 

 mass, bubbles, and a protruding opaque mass. 



3. Hyal ine spherule containing crystals. 



4. Dark mass with a hyaline body in- 

 cluding bubbles. 



5. Small hyalint- spherule. 



6. A composite opaque and hyaline grain 

 with bubbles and crystals. 



frequently include bubbles, patches of granular matter, and, more 

 rarely, crystals. The surfaces are usually smooth, and occasion- 

 ally bubble-like protuberances bulge out the sitles. Composite 

 grains are not uncommon in which a glassy mass protrudes from 

 an opaque body. Particles presenting these characters haxe been 

 obtained from iiouse-tops widelv separated from one another and 

 at considerable heights, as on the tower of the High Court — facts 

 which are of importance in considering any conclusions as to tlie 

 origin of this material." 



One member was of opinion that thev might have originated 

 as sparks from horseshoes in the streets, tiom the tram-lines, 



