and the Mode of its Communication. 53 



so regulate the distances of the hot bodies from their 



O 



respective balls that the bubble shall remain immov- 

 able in its place. 



In order to be able to ascertain precisely the tem- 

 peratures of the hot bodies presented to this instru- 

 ment, and in order that their surfaces might be equal, 

 two equal cylindrical vessels, of thin sheet brass, with 

 oblique cylindrical necks, were provided, of the form 

 represented in Figure 3 (Plate II.). 



This cylindrical vessel, which is placed in a horizon- 

 tal position in order that its flat bottom may be pre- 

 sented in a vertical position to one of the balls of the 

 thermoscope, is so fixed to a wooden stand, of a pecu- 

 liar construction, that it may be raised or lowered at 

 pleasure. This is necessary, in order that its axis may 

 be in the continuation of a line passing through the 

 centres of the two balls of the thermoscope. 



This cylindrical vessel is 3 inches in diameter and 4 

 inches in length, and its oblique cylindrical neck is 

 O.86 of an inch in diameter and 3.8 inches in length. 



The neck of this vessel is inserted obliquely into its 

 cylindrical body, in order that the water with which it 

 is occasionally filled may not run out of it, when the 

 body of the vessel is laid down in a horizontal posi- 

 tion, in the manner represented in the above-mentioned 

 figure. 



A thermometer, with a cylindrical bulb 4 inches in 

 length, being inserted into the body of this vessel, 

 through its neck, shows the temperature of the con- 

 tained water. 



Care is necessary, in constructing a thermoscope, to 

 choose a tube of a proper diameter; if its bore be too 

 small, it will be found very difficult to keep the spirit 



