272 Of the Propagation of Heat 



almost boiling hot. The result was just what I expected. 

 Two currents, in opposite directions, began at the same 

 instant to move with great celerity in the liquid in the 

 cylindrical tube, the ascending current occupying the 

 sides of the tube, while that which moved downwards 

 occupied its axis. 



As the saline liquor grew warm, the velocity of these 

 currents gradually diminished, and at length, when the 

 liquor had acquired the temperature of the surrounding 

 water in the jar, these motions ceased entirely. 



On taking the glass body out of the hot water, the in- 

 ternal motions of the liquor recommenced, but the cur- 

 rents had changed their directions, that which occupied 

 the axis of the tube being now the ascending current. 



When the cylindrical tube, instead of being held in a 

 vertical position, was inclined a little, the ascending cur- 

 rent occupied that side of it which happened to be upper- 

 most, while the under side of it was occupied by the cur- 

 rent which moved. (with equal velocity) downwards. 



When the contents of the glass body had acquired 

 the temperature of the air of the room, these motions 

 ceased ; but they immediately recommenced on exposing 

 the instrument to any change of temperature. 



In all cases where the instrument received Heat, the 

 current in the axis of its cylindrical tube when it was 

 placed in a vertical position (and that which occupied 

 its upper side when it was inclined) moved downwards. 

 When it parted with Heat, its motion was in an opposite 

 direction, that is to say, upwards. 



A change of temperature amounting only to a few de- 

 grees of Fahrenheit's scale was sufficient to set the con- 

 tents of the instrument in motion ; and the motion was 

 more or less rapid as the velocity was greater or less with 



