48 Mr. H. Tomlinson on the Thermoelectrical Properties 



B 2 S 2 are pieces of strong string fastened at Sj, S 2 to the ring 

 of a retort-stand weighted at the bottom. From A x passes 



a string over a pulley P, and to the end of this string a 

 weight of 1 kilo, was attached ; from A 2 passes another string 

 to a support so as to hold up the portion A 2 C of the wire A 2 , 

 B 2 . The two wires A! B 1? A 2 B 2 lie in the same horizontal 

 plane ; to the left of C they are covered with sand from C to a 

 distance of 10 centims. To the right of C for a distance of 

 about 3 centims. the wires are bare, but beyond this for 

 about 7 centims. are covered with sand ; the sand is sus- 

 tained on two stands placed to the right and left of C. 



First, the junction C was slightly heated by a burner, and 

 as the weight of 1 kilo, was not sufficient for the moderate 

 temperature then used to produce any sensible thermoelectrical 

 effect, the end A^ was pulled rather hard by the hand to 

 ascertain what would be the direction of the thermoelectrical 

 current due to the stress ; this direction was found to be from 

 the unstressed to the stressed wire through the hot junction, 

 as Thomson had already found. A rather large resistance 

 was then introduced into the galvanometer circuit for the 

 purpose of diminishing the sensibility of the instrument, and 

 the parts of the uncovered wires to the right of C were raised 

 to the temperature of bright red. Immediately this tempera- 

 ture was reached, there was a sudden start of the galvanometer- 

 needles, indicating that the stretched wire had suddenly lie- 

 come more negative relatively to the unstretched wire. When 

 the wires were allowed to cool there was, after a short pause, 

 an equally sudden deflection in the opposite direction. 



The weight of 1 kilo, was now supported by blocks placed 

 underneath it, and the junction C was again heated to a 

 bright red. At the critical temperature there was again a 

 sudden deflection, now indicating that the wire, which had 



