300 THE AMERICAN MONTHLY [Sept. 



acters, if any such there might have been; but most of 

 these studies were ineffectual until, about the month of 

 July of the past year, I took the matter up again and 

 finally succeeded in solving the mystery that had evaded 

 my previous attempts. The cue by which I unlocked the 

 secret, came about in this wise. It occurred to me to 

 trim down on a glass slip the burned end of a carbon 

 point, and over this dust rapidly stroking the back edge 

 of a pocket knife blade, during the experiment I noted a 

 peculiar frictional effect arise in driving the blade through 

 the carbon powder, and on submitting the slide thus 

 traversed by the strokes to the microscope I saw that 

 many fine lines were traced in the body of the glass as if 

 cut with a diamond splinter. Further expanding this idea, 

 I also remembered that a black carbon dust was period- 

 ically brushed out of the globes by the lamp trimmers on 

 their daily rounds, so I thought that I would also examine 

 this dust material under the microscope. With this in view 

 I engaged a lamp trimmer to secure for me a sample of 

 the carbon dust, brushed away daily as of no value, in 

 return for which service a small gratuity was given. I 

 thus secured several pounds of the dust, and was thus 

 enabled to study it from numerous points of view. I , 

 found the material to be made up of minute coke debris, 

 and myriads of minute glassy spherules, black, opaque 

 limpidly transparent. 



I found that the glass-like spherules if rolled be- 

 tween glass slips under good pressure, were seen to be 

 plowed up as if by a snow plow, a ridge of snowy white 

 glass powder being left in the wake of the rolling 

 spherule under pressure. I then conceived the idea of 

 testing the powder's abrading action on hard flint-like 

 minerals. For this purpose I made use of a small fragment 

 of an emery wheel heretofore used when preparing sur- 

 faces on the fossiliferous limestone or soft rock material. 



