26 Mr. Donovan on Galvanometric Deflections 



ciatiou of certain metals. This iron, when associated with bismuth, gives de- 

 flection on the same side of the magnetic meridian, whether it be heated 

 totally or partially ; yet iron becomes amenable to tin ; for heated partially, it 

 gives a deflection in the opposite direction to that which it causes when it is 

 lieated throughout its mass. Other instances might be adduced. 



Law XI. Under the consideration of the preceding Law it was shown that 

 many metals, when in the form of rods, produce opposite deflections according 

 as a part or the whole of the rod has been heated. It is now intended to be 

 shown that these deflections may be exhibited under circumstances apparently 

 amounting to a contravention of Law iv. These circumstances have been 

 much misunderstood ; it has been supposed that by merely elevating the tem- 

 perature of two active metals equally, they would produce deflection by con- 

 tact ; and the following facts apparently support that opinion. 



A wire of German silver one-eighth of an inch in diameter, and four feet in 

 length, was connected with one of the binding screws of the galvanometer, 

 without any interposed capillary rheophore ; a brass wire of the same thickness 

 and length was similarly connected with the other binding screw ; the farther 

 ends of the two wires were tied together with thread. The tied ends were 

 then plunged in boiling water, which immediately produced a deflection of 50° 

 west. 



The same experiment was made with much thinner wires of these metals, 

 with exactly the same results. 



From each of the first-mentioned pair of wires twelve inches were cut off", 

 and their ends were connected with the binding screws, in the same order as 

 before, by means of capillary copper wires. The two farther ends bent to each 

 other were tied together with thread, and about an inch of the ends so tied was 

 immersed in boiling water. The deflection was west as before. 



In this state of things the pair of connected wires was suddenly and totally 

 immersed in boiling water. The needle passed eastward, thus showing, in 

 conformity with what has been explained, Law x., the difierence of deflection 

 produced by partial and total heating of the metals. Other associations of 

 metals were also tried ; bismuth and antimony succeeded best. A rod of each, 

 twelve inches long, and a quarter of an inch in diameter, was prepared ; they 

 were tied together at one end with thread in the form of the letter V; the free 



