114 Britain's Heritage of Science 



both its points of electrization. There was a vio ent 

 effervescence at the upper surface; at the lower, or 

 negative surface, there was no liberation of electric 

 fluid; but small globules having a high metallic lustre, 

 and being precisely similar in visible characters to quick- 

 silver, appeared, some of which burnt with explosion 

 and bright flame, as soon as they were formed, and others 

 remained, and were merely tarnished, and finally covered 

 by a white film which formed on their surfaces." 

 Sodium was similarly obtained from soda. 

 The interest which the announcement of the discovery 

 of two new elements created throughout the scientific world 

 was accentuated by the peculiar properties which distin- 

 guished them from all known metals. They are both lighter 

 than water, and when brought into contact with that liquid 

 burst into flame, owing to their great affinity for oxygen. 

 The investigation of their chemical properties was most 

 difficult, because they oxidize rapidly when exposed to air, 

 and can only be preserved by being immersed in naphtha 

 or some similar liquid. Though a serious illness interrupted 

 Davy's work, he continued to give the Bakerian lecture 

 for six successive years, each time adding something to 

 our knowledge, mainly in connexion with the researches 

 which have already been described. He received the honour 

 of knighthood in 1812, and shortly afterwards informed the 

 managers of the Royal Institution that he could not pledge 

 himself to continue his lectures, but was prepared to retain 

 his position as Professor of Chemistry and Director of the 

 Laboratory without salary. This offer was accepted. In 

 the same year he published his " Elements of Chemical 

 Philosophy," in which he described the " Voltaic Arc," that 

 column of light which is formed between carbon points when 

 a current of sufficient electromotive force is passed between 

 them. Even Davy's vivid imagination could hardly have 

 foreseen the part which this discovery was to play in the 

 future history of illumination. The same paper contains 

 another important result. Partly anticipating the subsequent 

 work of Ohm, the electric resistance of a conductor was 

 shown to be proportional to its length directly, and inversely 

 to its cross-section. 



