236 Royal Society. 



in a state of perfect equilibrium, any portion of it contained in a 

 vertical tube would of course be perfectly stationary unless some 

 adventitious cause produced disturbance of its equilibrium. But 

 our atmosphere being a mixed fluid, and the a(jueous vapour being 

 of a much lower specific gravity at all atmospheric temperatures 

 than the compound of which it forms a part, it is constantly rising 

 within a tube, as in the free air ; entering at the lower, and making 

 its exit at the upper orifice of the tube. 



The experiments appear further to demonstrate, that the presence 

 of aqueous vapour in the atmosphere is essential to the production 

 of the current within the vertical tubes, since by the abstraction of 

 vapour from the air by quicklime, the rotations of the discs were 

 invariably either diminished or caused to cease ; while on the other 

 hand, when the proportion of aqueous vapour in the air was in- 

 creased, the currents and the rotations of the discs were simulta- 

 neously accelerated. 



In concluding the details of these experiments, the author considers 

 that they all tend to prove the existence of an upward current, under 

 the circumstances described in the commencement of this paper. 



They moreover yield a series of results which he hopes the Society 

 will deem to be not without interest. 



These results show it to be probable, if not certain, that the ordi- 

 nary temperature of air within tubes, under the circumstances in 

 which these were placed, is higher than of that external to them, all 

 other relations of the tubes and surrounding objects being the same ; 

 they also show, that in eight instances, when the thermometers in- 

 dicated an equality of temperature, within and external to the tube, 

 the rotations of the discs still continued ; and that when four coils 

 of tape, moistened with water, were applied round the external sur- 

 face of the tube, the rotations of the disc did not wholly cease. 



They also show, that when the atmosphere of the room, in which 

 the tubes were immersed, contained a larger or smaller proportion of 

 aqueous vapour, all other things being equal, the discs revolved with 

 more or less velocity ; but that when the atmosphere was deprived 

 in a great degree of aqueous vapour by the presence of quicklime, 

 the thermometric state in all other respects remaining the same, the 

 revolutions of the discs ceased. 



Adverting to the indications cited above, of a minute excess of 

 temperature in the interior of the tubes, and assuming that even 

 that slight excess would be sufficient to rotate the discs, still the 

 rotations diminished or ceased in proportion as the aqueous vapour 

 was withdrawn. 



Any increase of temperature which might have been produced by 

 the quickhme would have had a tendency rather to increase than 

 diminish the revolutions of the discs, but we have seen that the 

 abstraction of the vapour entirely arrested their rotation. 



"With regard to the specific influence of each of the circumstances 

 and agents most probably concerned in producing the phenomena 

 described above, such as protection of the air within the tube from 

 lateral expansion and mechanical agitations, to which the external 



