488 M. H. Weber on the Heat-conducting Power 



points. In the places H and I, at the distances \l and ^l from 

 the end of the bar^ two German-silver wires were soldered to the 

 iron bar, two iron wires to the German-silver one; and their 

 ends, at about 6 inches from the bar, were soldered to two copper 

 wires which led to the same galvanometer as the wires before 

 mentioned. In front of the galvanometer was a regulator such 

 that now the conduction to the middle of the bar, and now the 

 conduction to the places H and I could be connected with the 

 galvanometer. Each of the thermo-currents circulating in the 

 two conductions could be passed in opposite directions through 

 the galvanometer; and, finally, it was also possible to shut off 

 the galvanometer and to determine the stationary position of the 

 needle at any moment. If the conduction to H and I was con- 

 nected with the galvanometer, the intensity of the thermo-current 

 circulating in this circuit was evidently proportional to the dif- 

 ference between the temperatures of H and I. The bar and the 

 cocks were in a room by themselves, the galvanometer and the 

 two steam-boilers were in two adjoining rooms. The pipes for 

 steam and water were carried through the dividing wall, and 

 wrapped tightly round with strips of cloth and tow. In this 

 manner any considerable alteration of temperature of the air 

 surrounding the bar during the experiments was avoided. 



The Galvanometer and its Employment, 



The galvanometer made use of in the experiments was con- 

 structed according to the rules for attaining the maximum of 



sensitiveness*. The length of the needle was 100 milhms. ; and 



the multiplier had a resistance of 0*59064 x 10^° -^r- at a 



second 



temperature of 10° C. When the galvanometer was shut off, 



the arresting-power was so great that the needle returned from 



deflections of 12° to the position of rest after two oscillations. 



Hence the logarithmic decrement X could not be determined 



immediately from the diminution of the arc of oscillation, but 



had to be deduced from a series of observations in which different 



known resistances were inserted. For it the following value 



was found : — 



X=4-2458. 



The time of an oscillation with the circuit open was 4'''466. 



Now, for all galvanometers constructed according to the direc- 

 tions above mentioned, the torsion-moment can be determined 

 which is exerted by the multiplier upon the needle deflected to 

 an angle <^ from the plane of the meridian when a current of the 

 intensity I flows through the multiplier. For, denoting this 

 * Pogg. Ann. vol. cxxxvii. p. 121. 



