in the Metallic Cross. 47 



the reduction of temperatures of metallic joints by electrical 

 currents j and as it readily gave a galvanometer indication cor- 

 responding with the effect that would be derived from cooling the 

 central joint by artificial means, the experiments with this cross 

 have been much used to prove the reduction of the temperatures 

 of joints by electrical currents. On this head the experiments I 

 published in the April Number, vol. v. p. 193, to show that the 

 calorific effects in the cell of a battery may be exhibited in the 

 joints of a metallic circuit in connexion with it, explain the reduc- 

 tion of the temperatures of these joints in a manner consistent 

 with recognized laws ; while the facts shown in the present expe- 

 riments give a new explanation to 

 the phenomena presented to us in 

 the metallic cross. The annexed 

 diagram represents the cross, in 

 which AC and BD are two bars 

 of metal soldered or fastened in 

 good metallic contact at E. From 

 the extremities of these bars at A 



and D wires were used to form a connexion with Smee's bat- 

 teries ; the other extremities of the bars at B and C were by 

 wires connected with a galvanometer. When the electricity from 

 a battery was made to circulate in the direction AED, AC being 

 the bismuth bar, an electrical current was generated in the other 

 pair of arms moving in the direction BEC, or opposite to the pri- 

 mary current ; being the same in effect as would be obtained by 

 cooling at E by artificial means, — a result which was uniform for 

 all degrees of intensities of primary currents. On my recent 

 return to these experiments I verified this observation, and found 

 that, change the intensity and quantity of the current how you 

 will, so long as it moved in the direction AED, the action on the 

 galvanometer was the same as if the joint E was cooled. I felt 

 certain that many of the currents I had passed had heated the 

 metals at E ; and to try this point, a delicate thermometer was 

 tied down on the central part E of a bismuth and antimony cross. 

 A feeble galvanic current from a single pair of Smee's plates, 

 acted on by a battery a little lower in temperature than that of 

 the atmosphere, reduced the thermometer on the joint 1° ; but 

 when the extent of the surface of the battery in action was 

 increased, the thermometer rose above the atmospheric tempera- 

 ture ; and with a further increase of surface of battery in action, 

 there was a rise of temperature till the heat of the joint stood 

 15° higher than that of the surrounding atmosphere. Now 

 while this was the case, the galvanometer indicated that the 

 joint E was cooled, consequently it did not represent the 

 thermo-electrical current generated there. When formerly en- 



