266 



of the first-mentioned metal, it being in contact with the 

 second, as will balance or destroy the tendency to deflection 

 on either side of the magnetic meridian ; the needle will then 

 hesitate near the zero, and there will be no decided deflection. 



XIII. If two difi'erent metals, properly connected with 

 the galvanometer, be placed in contact with each other at 

 one point ; and if a corresponding small portion of each be 

 brought to an equal temperature, different from that of their 

 respective remainders, they will produce deflection on the 

 side of the magnetic meridian opposite to that on which the 

 deflection would have temporarily taken place, had the metals 

 been throughout their mass exposed to that temperature. If 

 the portions of the metals acted on be raised above the tem- 

 peratures of their remainders, the deflection will be on the 

 side of the magnetic meridian opposite that to which the 

 needle will be deflected, if these parts be reduced to a tempe- 

 rature below that of their remainders. 



XIV. The deflection produced by thermo-contact or attri- 

 tion will be always reversed when the exciting metals con- 

 nected with the extremities of the galvanometer coil are trans- 

 posed. 



XV. When deflection is produced in consequence of the 

 attrition or contact of two metals, one of which is adequately 

 hotter than the other, the deflection will change to the oppo- 

 site side of the magnetic meridian, if the hotter metal be cooled, 

 and the cooler metal be adequately heated, the contact or 

 attrition being continued as at first. 



XVI. The deflection produced by the mutual attrition of 

 any particular pair of metals will take place, at all temperatures 

 of these metals, on the same side of the magnetic meridian, 

 provided that the temperature be equal or nearly equal in 

 both. As this direction of the needle is always the result of 

 the attrition of these particular metals when they are in their 

 ordinary state of equality of temperature, it may conveniently 

 be called the natural deflection of any pair of metals ; it is 



