132 Experimental Investigations 



diameter is five inches, and its height six. It is one 

 inch and a half in diameter, and six inches high. Its 

 neck is one inch and a quarter in diameter, and two 

 inches and a half long. 



The interior vessel is suspended in the centre of the 

 external one by a stopper of cork. This stopper is 

 adjusted to the neck of the external vessel, and there is 

 a cylindrical hole of three quarters of an inch diameter 

 through the cork, and having the same axis ; which per- 

 foration receives the neck of the interior vessel, and 

 retains it in its place. 



The interior vessel was introduced and fixed in its 

 place before the bottom of the exterior vessel was sol- 

 dered in. 



At the centre of the bottom of the great vessel is a 

 small metallic tube, of three quarters of an inch diame- 

 ter and one inch and a half long, by means of which 

 this instrument is attached to a solid heavy foot of 

 metal, which supports it in a vertical position when the 

 whole instrument is submerged in a vessel of water. 



This instrument, which greatly resembles that de- 

 scribed in my seventh Essay on the Propagation of 

 Heat in Fluids, which I have called the passage ther- 

 mometer* may be used to make a number of interesting 

 experiments on the cooling of bodies through different 

 fluids. In the present experiment I employed it in the 

 following manner : 



The interior vessel was entirely filled with hot water 

 to the height of half an inch in its neck, and a good 

 thermometer, having its cylindrical bulb four inches 

 long, was inserted therein. The instrument was then 

 plunged in a mixture of pounded ice and water, and 



* See Vol. I. p. 237. 



