278 FRAGMENTS OF SCIENCE. 



to dry it, and to remove its carbonic acid, carried into the 

 experimental tube a considerable amount of mechanically 

 suspended matter, which was illuminated when the beam 

 passed through the tube. The effect was substantially the 

 same when the air was permitted to bubble through the 

 liquid acid and through the solution of potash. 



Thus, on October 5, 1868, successive charges of air were 

 admitted through the potash and sulphuric acid into the ex- 

 hausted experimental tube. Prior to the admission of the 

 air the tube was optically empty ; it contained nothing 

 competent to scatter the light. After the air had entered 

 the tube, the conical track of the electric beam was in all 

 cases clearly revealed. This, indeed, was a daily observa- 

 tion at the time to which I now refer. 



I tried to intercept this floating matter in various ways ; 

 and on the day just mentioned, prior to sending the air 

 through the drying apparatus, I carefully permitted it to 

 pass over the tip of a spirit-lamp flame. The floating mat- 

 ter no longer appeared, having been burnt up by the flame. 

 It was, therefore, of organic origin. I was by no means 

 prepared for this result ; for I had thought that the dust of 

 our air was, in great part, inorganic and non-combustible. 



I had constructed a small gas-furnace, now much em- 

 ployed by chemists, containing a platinum tube, which 

 could be heated to vivid redness. 1 The tube contained a 

 roll of platinum gauze, which, while it permitted the air to 

 pass through it, insured the practical contact of the dust 

 with the incandescent metal. The air of the laboratory 

 was permitted to enter the experimental tube, sometimes 

 through the cold, and sometimes through the heated, tube 

 of platinum. The rapidity of admission was also varied. 

 In the first column of the following table the quantity of 

 air operated on is expressed by the number of inches which 

 the mercury gauge of the air-pump sank when the air en- 



1 Pasteur was, I believe, the first to employ such a tube. 



