HISTORY OF GALVANISM. 95 



probably be sufficient ; but where the resistance of 

 imperfect conductors is to be overcome, the com- 

 bination must be great, but the size of the plates \s 

 must be small. But if quantity and intensity be 

 both required, then a great number of large plates 

 will be necessary. For general purposes, four 

 inches square will be found to be the most conve- 

 nient size.* 



Mr. Children has since constructed a still larger More pow* 

 and more powerful battery, consisting of 20 pairs ry^isia*" 

 of copper and zinc plates, each plate being six feet 

 by two feet eight inches. It ignited six feet of thick 

 platina wire, and melted platina with great faci- 

 lity ; it also melted iridium and osmium. At the 

 suggestion of Dr. Wollaston, a singular fact was 

 ascertained, that a greater length of thick platina 

 wire was ignited, than of platina wire of a much 

 smaller size.f 



About this time a^battery of very great power Battery at 

 was constructed at the Royal Institution. It institution, 

 consisted of 200 separate parts, each part com- 

 posed of 10 double plates, and each plate con- 

 taining 32 square inches, the whole of the double 

 plates being 2,000, and the whole surface 128,000 / 



square inches. When the whole series was put 

 into action, platina, quartz, sapphire, magnesia, 

 and lime, were all rapidly fused ; while diamond, 



* Phil. Trans, for 1809- p. 32. 

 f Annals of Philosophy, it. 147. 



