in Fluids. 245 



This tube, which is -fa of an inch in diameter inter- 

 nally, and very thin, is composed of very transparent, 

 colourless glass, which rendered the appearance clear and 

 distinct and exceedingly beautiful. On examining the 

 motion of the spirits of wine with a lens, I found that 

 the ascending current occupied the axis of the tube, and 

 that it descended by the sides of the tube. 



On inclining the tube a little, the rising current moved 

 out of the axis and occupied that side of the tube 

 which was uppermost, while the descending current occu- 

 pied the whole of the lower side of it. 



When the cooling of the spirits of wine in the tube 

 was hastened by wetting the tube with ice-cold water, the 

 velocities of both the ascending and the descending cur- 

 rents were sensibly accelerated. 



The velocity of these currents was gradually lessened 

 as the thermometer was cooled, and when it had acquired 

 nearly the temperature of the air of the room, the mo- 

 tion ceased entirely. 



By wrapping up the bulb of the thermometer in furs, 

 or any other warm covering, the motion might be great- 

 ly prolonged. 



I repeated the experiment with a similar thermometer 

 of equal dimensions, filled with linseed-oil, and the ap- 

 pearances, on setting it in the window to cool, were just 

 the same. The directions of the currents, and the parts 

 they occupied in the tube, were the same, and their mo- 

 tions were to all appearance quite as rapid as those in the 

 thermometer which was filled with spirits of wine. 



Having now no longer any doubt with respect to the 

 cause of these appearances, being persuaded that the mo- 

 tion in these liquids was occasioned by their particles 

 going individually , and in succession, to give off their Heat 



