On a Method of exhibiting fine Galvanometric Experiments . 109 



stituents enumerated, they were both tested for chromium and 

 zinc ; the oxide of the former metal, being isomorphous with 

 sesquioxide of iron, might possibly have been present as in the 

 mineral chrome iron. Zinc also is known to occur in Frank- 

 linite, a mineral of the magnetic oxide type, in which part or the 

 whole of the protoxide of iron is replaced by the corresponding 

 oxide of zinc. Neither of these metals, however, were found to 

 be present. 



Babylonian. 



•72 2^62 



Specific gravity . . . 4-94 5-02 



Formula. (lOFe^O^ + Fe^O^, FeO) . Fe^O^. 

 From this statement, it will be seen that the materials of the 

 cylinders and amulet agree in chemical composition, as in hard- 

 ness and specific gravity, with known varieties of native magnetic 

 oxide of iron and haematite ; their manufacture from these mine- 

 rals cannot therefore be any longer a matter of doubt. 

 London, January 9, 1856. 



XIII. On a Method of exhibiting fine Galvanometric Experiments 

 to a large audience ; extracted from a Letter from M. du Bois 

 Reymond to M. Magnus*. 



WE have so often spoken together of the difficulty of show- 

 ing fine galvanometric experiments to a large audience, 

 that I believe it will interest you to learn that I have at length 

 succeeded in completely surmounting this difficulty. I have 

 been able to show my finest experiments on animal electricity, 

 * Translated from PoggendorfF's Annalen, vol. xcv. p. 607. 



