136 Royal Imilliition. 



Otto de Giiericke, Boyle, Haw kesbee, oic. observed that 

 luminous appearances were exhibited by electrified bodies, 

 and for a series o^ years these novel exhibitions served rather 

 to amuse scieniifio men than to direct them Lo the funda- 

 mental principles of eleclriciiv. 



The discovery of Franklin, that ligbtninsi depends on 

 the electrical state of the atmosphere, gave a new impulse 

 to this department of knowledge ; and the novel facts ob- 

 served by Galvani led to the noble inventions of Volta. 

 " The discoveries to which they led," says Mr. Daw, " have 

 produced a new order and arrangement of facts, and have 

 to a certain extent connected together mechanical and che- 

 mical science, and exhibited new and unex(iected proper- 

 ties of material bodies." 



The Professor said, that, in treating; of the subject he 

 should offer views different from any that have been de- 

 veloped by elementary writers on electricity ; but no apology 

 was necessary, the progressive nature of science is one of 

 its noblest characters. As the facts of electricity have mul- 

 tiplied, the theory is more capable of being simplified ; a 

 number of effects formerlv supposed to be insulated may 

 be attributed to the same cause. 



Mr. Davy described the different modes in which elec- 

 tricity is excited, by the contact of bodies, by friction, by 

 heat and changes of their form ; and this property seems 

 to belong to all material substances. 



In the mineral kmgdom there are several stones which 

 exhibit electrical effects bv being heated, as the tourmaline, 

 boracite, See. Dry vecetable substances and most crys- 

 tallized bodies produce these phenomena by friction, and 

 the metals by contact. ' Thus zinc made to touch mercury 

 becomes positive, the mercury is negaiive. The case is the 

 satue with other metals, as gold and mercury, copper and 

 mercurv, &c. Even fluids and metals produce similar ef- 

 fects, as in the case of liver of sulphur and copper. 



The electrical effects produced by the contact of different 

 melals are less obvious than those connected with luminous 

 appearances', but thev may be perceived bv the sensations, 

 or by the effects produced on the limbs of cold-blooded 

 animals recentlv deprived of life, as in the celebrated ex- 

 periment of Galvam, who conceived that the effect was 

 produced bv a ?pceific subtile iluid; but the genius ot \''olta, 

 said Mr. Davy, proved that it was electrical, and gave the 

 demonstration of us principles in one of the noblest inven- 

 tions ever produced by hmnan sagacitj. 



" V^ery slight circumstances," said the Professor, " are 

 sufficient to develop these important powers of matter, and 



they 



