24 Biographical Memoir of Sir Humphry Davy. 



had been unrolled, the sentiments of the conservators underwent 

 a sudden change, and so many impediments were thrown in the 

 way of farther investigation, that the undertaking was entirely 

 abandoned. This journey afforded to Mr Davy an opportunity 

 of investigating a subject of interest in the history of the arts, 

 viz. the nature of the colours used in painting by the ancients. 

 Some on the walls of Pompei or Herculaneum were sufficient to 

 form the subject of analysis. He found that they were nearly 

 as numerous as our own, and that many seemed to have been 

 even better prepared, since they had resisted the effects of time 

 for so many ages *. 



This journey likewise supplied many new observations on 

 volcanoes -f*, but which always bore relation to the ideas he had 

 previously embraced. The excessive incandescence of lava at 

 the moment of its ejection, the noise that precedes it, and the 

 water, salts, and exhalations by which it is accompanied, all 

 tended to confirm the idea he had entertained from the time of 

 his first experiments on alkalies, that the principal cause of 

 these remarkable phenomena is the action of sea- water on metals, 

 which he supposes to exist, not yet oxidized, in the interior of 

 the earth. This supposition reconciled a great variety of views 

 on the primitive state of the globe, and the various changes 

 which its surface has undergone, by which he sought to unite 

 in a single system all the observations of later times relating to 

 the subject, from those of Herschel on nebulae, to those of the 

 latest naturalists on the nature and relative position of earthy 

 deposits, and on the remains of animals and vegetables which 

 they contain. 



These hypotheses were not unworthy of a genius which had 

 made so many real discoveries, but he did not assign to them 

 the importance of truths of the first order. He did not give 

 them to the world till the publication of a work in which his 

 imagination expatiates on numerous other subjects and of a 

 much higher nature, his Consolations in Travel^ the last of his 



• Some experiments and observations on the colours used in painting by 



the ancients Roy. Soc. Lond. 23d February 1815. Phil. Trans, vol. cv^ 



p. 97. Ann. de Chim. tom. xcxvi. p. 72. and 193. Biblioth. Brit. vol. lix. 

 p. 226. and 336, and Ix. p. 129. 



f On the phenomena of Volcanoes. — Roy. Soc. Lond. 20th May 1828. 



Phil Trans, vol. cxviii. p. 241 Ann. de Chimie et de Physique, vol. xxxviii. 



p. 133 Biblioth. Univ. voL xxxix. p. 121. 



