DISCOVERY BY MEANS OF INSTRUMENTS OF GREAT POWER. 561 



battery composed of very large plates, that Trommsdorff, in 

 the year 1803, discovered the voltaic combustion of thin 

 leaves of metal. Mr. Children also, by the aid of such an 

 instrument, in the year 1809, was enabled to melt the 

 most refractory substances, including platinum, osmi- 

 iridium, the oxides of uranium, molybdenum, tungsten, 

 cerium, titanium, and tantalum. By means of the cur- 

 rent from a powerful voltaic battery, Davy, in the year 

 1806, first isolated the alkali metals, and truly discovered 

 them. By similar means, in the year 1813, he discovered 

 the c voltaic arc,' or convective discharge of voltaic elec- 

 tricity, and melted magnesia, lime, sapphire, and various 

 other extremely infusible substances. By trying the effect 

 of a powerful magnet upon that discharge, he also, in the 

 year 1820, discovered the magnetic character and rotation 

 of the voltaic arc. 



In the year 1836, Crosse, by employing a great number 

 of cells of a water battery, was enabled to artificially pro- 

 duce a number of different minerals. Grassiot also, in 

 more recent times, by using similar but more powerful 

 means, discovered that the electric discharge of the bat- 

 tery would pass through atmospheric air previous to mak- 

 ing any contact of the poles of the battery. W. De la Rue 

 also, by employing a highly insulated series of 10,000 cells, 

 each cell being composed of zinc and chloride of silver 

 excited by a solution of salammoniac, has discovered quite 

 recently some of the laws, and a number of additional 

 phenomena, relating to that discharge. 



The discovery of electro-magnetism by Oersted, in the 

 year 1819, enabled very powerful magnets to be made, 

 and thus paved the way for discoveries to be evolved by 

 their aid. It was by the employment of such magnets 

 that Faraday was enabled to discover diamagnetism, the 

 universality of magnetism, and the magnetic rotary 



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