172 Prof. J. Tyndall on the [Jan. 13, 



forated in the middle by a hole 2 inches in diameter, closed air-tight by 

 a sheet of india-rubber. This sheet is pierced in the middle by a pin, 

 and through the pin-hole is passed the shank of a long pipette ending 

 above in a small funnel. A circular tin collar, 2 inches in diameter and 

 1 j inch high, surrounds the pipette, the space between both being packed 

 with cotton-wool moistened by glycerine. Thus the pipette, in moving 

 up and down, is not only firmly clasped by the india-rubber, but it also 

 passes through a stuffing-box of sticky cotton-wool. The width of the 

 aperture closed by the india-rubber secures the free lateral play of the 

 lower end of the pipette- Into two other smaller apertures in the top of 

 the cupboard are inserted, air-tight, the open ends of two narrow tubes, 

 intended to connect the interior space with the atmosphere. The tubes 

 are bent several times up and down, so as to intercept and retain the 

 particles carried by such feeble currents as changes of temperature might 

 cause to set in between the outer and the inner air. 



The bottom of the box is pierced, sometimes with two rows, sometimes 

 with a single row of apertures, in which are fixed, air-tight, large test-tubes, 

 intended to contain the liquid to be exposed to the action of the mote- 

 less air. 



On the 10th of September the first case of this kind was closed. The 

 passage of a concentrated beam across it through its two side windows 

 then showed the air within it to be laden with floating matter. On the 

 13th it was again examined. Before the beam entered and after it 

 quitted the case its track was vivid in the air, but within the case it 

 vanished. Three days of quiet sufficed to cause all the floating matter 

 to be deposited on the sides and bottom, where it was retained by a 

 coating of glycerine, with which the interior surface of the case had been 

 purposely varnished. The test-tubes were then filled through the pipette, 

 boiled for five minutes in a bath of brine or oil, and abandoned to the 

 action of the moteless air. During ebullition aqueous vapour rose from 

 the liquid into the chamber, where it was for the most part condensed, 

 the uncondensed portion escaping, at a low temperature, through the bent 

 tubes at the top. Before the brine was removed little stoppers of cotton- 

 wool were inserted in the bent tubes, lest the entrance of the air into the 

 cooling chamber should at first be forcible enough to carry motes along 

 with it. As soon, however, as the ambient temperature was assumed by 

 the air within the case the cotton-wool stoppers were removed. 



"We have here the oxygen, nitrogen, carbonic acid, ammonia, aqueous 

 vapour, and all the other gaseous matters which mingle more or less 

 with the air of a great city. We have them, moreover, " untortured " 

 by calcination and unchanged even by filtration or manipulation of any 

 kind. The question now before us is, can air thus retaining all its 

 gaseous mixtures, but self-cleansed from mechanically suspended matter, 

 produce putrefaction ? To this question both the animal and vegetable 

 worlds return a decided negative. 



