Strain on the TJiermo-el^tric Qualities of Metals. 171 



ticity. AB is a brass tube throiigh which steam from a kettle is allowed 

 to pass. The wire under test is wound round this brass tube three times, 

 and then round a small brass tube in the triangular frame below, and 

 then to one of the terminals of the galvanometer. The wire is thus 

 quite continuous, from one terminal of the galvanometer to the other 

 terminal. Some cotton wool is loosely packed at the hot junction of 

 the wire to ensure that the temperature of the wire is at steam tem- 

 perature. The weight of the triangular frame (two sides wood and 



Fia. 3. 



To GAlfano/reCer. 



one side brass tube) with its hook for hanging weights on was 220 

 granames. This is the smallest weight used for each wire, every 

 one of which was about No. 30 S.W.G. (diameter, 0'0315 cm.). The 

 object of the small brass tube in the triangular frame was to keep 

 the temperature of the cold junction at any determined temperature by 

 allowing water or other fluid to flow through it. In all the experi- 

 ments hitherto made, the temperature of the cold junction was taken as 

 the temperature of the air at the time of each observation. 



§ 12. The experiments were performed as follows : — The wire was 

 put into the circuit, as shown in fig. 3. After steam was allowed to 

 pass through the tube for some time, the galvanometer reading and the 

 air temperature were taken. The circuit was then broken, and the 

 metallic zero of the galvanometer was noted. The circuit was made, 

 and a weight was added on to the hook of the triangular frame. Three 

 readings of the galvanometer were now taken : (1) with the weight on, 

 (2) with the weight off, and (3) with the circuit broken. A heavier 

 weight was hung on, and other three readings taken, and so on to the 

 heaviest weight used in the experiments. 



§ 13. The readings of the galvanometer were in the same direction 



