Reflections on Heat. 175 



By means of a little glass reservoir, an inch in length 

 and a line in internal diameter, inserted in the tube at 

 one of the elbows, there is introduced into the interior 

 of the instrument a small quantity of coloured spirit 

 of wine (exactly enough to fill the reservoir without 

 interfering with the free passage of the air from one 

 bulb to the other) ; this being done, the extremity of 

 the reservoir is sealed hermetically, and all communica- 

 tion between the air enclosed in the instrument and the 

 air of the outside atmosphere is forever interrupted. 



The instrument is adjusted and prepared for use as 

 follows : 



The bulb which is farthest from the reservoir having 

 been warmed slightly with the hand, the instrument is 

 suddenly turned over, so as to bring the reservoir 

 uppermost, and in this way a small quantity of the 

 spirit of wine passes from the reservoir into the hori- 

 zontal part of the tube ; restoring immediately the in- 

 strument to its natural position, the observer withdraws 

 himself from it, and waits for the small quantity of 

 spirit of wine which has passed into the horizontal part 

 of the tube to become stationary ; this will be as soon 

 as the two bulbs have acquired the same temperature. 



The little bubble of spirit of wine, wh'ch serves as 

 the index of the instrument, and which may be about 

 three quarters of an inch long, should become station- 

 ary nearly in the middle of the horizontal portion of the 

 tube ; if it is too near either of the elbows it must be 

 returned to the reservoir, and the operation performed 

 anew. 



When this delicate operation is finished, the instru- 

 ment is ready for use. The method of employing it is 

 as follows : 



