DUST AND DISEASE. 283 



charged with floating matter ; at the end of half an hour it 

 was optically empty. 



A second experiment was thus arranged : on the wooden 

 base of a cubical glass shade, measuring 11|- inches a side, 

 upright supports were fixed, and from one support to the 

 other 38 inches of platinum wire were stretched in four 

 parallel lines. The ends of the platinum wire were soldered 

 to two stout copper wires, which passed through the base 

 of the shade and could be connected with a battery. As 

 in the last experiment, the shade rested upon cotton-wool. 

 A beam sent through the shade revealed the suspended 

 matter. The platinum wire was then raised to whiteness. 

 In iive minutes there was a sensible diminution of the mat- 

 ter, and in ten minutes it was totally consumed. This 

 proves that when the platinum wire is sufficiently heated, 

 the floating matter, instead of being distributed, is destroyed. 



But is not the matter really of a character which permits 

 of its destruction by the moderately-heated platinum wire ? 

 Here is the reply : 



1. A platinum tube, with its plug of platinum gauze, 

 was connected with an experimental tube, through which a 

 powerful beam could be sent from an electric lamp placed 

 at its end. The platinum tube was heated till it glowed 

 feebly but distinctly in the dark. The experimental tube 

 was exhausted, and then filled with air which had passed 

 through the red-hot tube. A considerable amount of float- 

 ing matter which had escaped combustion was revealed by 

 the electric beam. 



2. The tube was raised to brighter redness and the air 

 permitted to pass slowly through it. Though diminished 

 in quantity, a certain amount of floating matter passed into 

 the exhausted experimental tube. 



3. The platinum tube was rendered still hotter ; a 

 barely perceptible trace of the floating matter now passed 

 through it. 



