472 



saucer, containing concentrated sulphuric acid, wasal so placed under 

 the bell-glass, on a level with the orifice of the tube. The rotations 

 of the disc were accelerated by placing the warm hand for a few 

 seconds in contact with the long branch of the tube ; but at the end 

 of five minutes after it was withdrawn, and the room left and closed, 

 the disc had ceased to rotate. 



To determine the influence of partial abstraction of aqueous 

 vapour from the entire atmosphere of the room on the velocity of 

 the rotations, the three tubes, with long limbs of 12, 24, and 48 

 inches, employed in a previous experiment, were placed near each 

 other, and three bushels of quicklime were spread in shallow vessels 

 on the floor and other parts of the room. Before the lime was placed, 

 the disc in the 12-inch tube was revolving at the rate of 0'75 per 

 minute; that in the 24-inch tube at 2'0; and that in the 48-inch 

 tube at 4'0 per minute. At the end of fifty minutes the rotation had 

 ceased in the 12-inch tube, and was reduced to 1*75, and 3*5 in' the 

 24- and 48-inch tubes. After seventy minutes, rotation had ceased 

 in the 24-inch tube, and was reduced to 3' 75 in the 48-inch tube. 

 Finally, after ninety minutes, the rotations in the 48-inch tube were 

 reduced to 2' 7 5 per minute. 



Similar reductions in velocity were observed after the removal 

 and reintroduction of the quicklime in a second and third series of 

 observations. Thus in all these experiments the rotations in the 

 12- and 24-inch tubes entirely ceased; and those in the 48-inch 

 tube, although continued, were much diminished ; a result most pro- 

 bably attributable to the greater quantity of aqueous vapour remain- 

 ing in the upper strata of the air in the room. 



The mean depression of the wet-bulb thermometer, the hygro- 

 meter being placed 48 inches above the floor, and the lime being 

 absent, was 3*2 ; when the lime was present, 3*4. When the hygro- 

 meter was on the floor the depression of the wet bulb was 3 '5. 



As the abstraction of aqueous vapour from the atmosphere dimi- 

 nished and even abolished the currents of air within the tubes, it 

 was to be expected that increase of vapour in the atmosphere would 

 produce the contrary effect, and accelerate the currents and the cor- 

 responding revolutions of the discs, and the following results coin- 

 cide with that expectation. 



In the first experiment, the tube and bell-glass previously described 



