334 Hoyal Society : — 



the rotations, the three tubes (figs. 7, 8, 9), with long limbs of 12, 24, 

 Fig. 17. Fig. 18. 



and 48 Inches, employed in a previous experiment, were placed near 

 each other, and three bushels of quickhme 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; thar 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 l'7r>, and 3'5 in the 

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

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

 Finally, after ninety minutes, the rotations in the 48-inch tube wei'e 

 reduced to 2-75 per minute. 



Similar I'eductions 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 inclies above the floor, and the lime being 

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

 hygrometer 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 eff^ect, and accelerate the cunents and the cor- 

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

 cide with that expectation. 



