20 Sir C. Lyell 07i the Submarine Origin of Teneriffe 



the different stages of oxidation of nitrogen), this gradually dis- 

 appears and the other gas alone remains. 



III. If the gases are composed of oxygen and a solid simple 

 substance, complete decomposition by the current only takes 

 place gradually, while the oxygen goes to the platinum of the 

 negative electrode (sulphurous acid, carbonic oxide, carbonic 

 acid). Carbonic acid is instantly decomposed into the gaseous 

 lower stage of oxidation and into free oxygen, which gradually 

 goes to the platinum (I). The carbonic oxide is gradually decom- 

 posed by the oxygen leaving the carbon and combining with the 

 negative electrode*. 



Bonn, August 25, 1858. 



III. Remarks on Professor C. Piazzi Smyth's supposed proofs 

 of the Submarine origin of Teneriffe and other Volcanic Cones 

 in the Canaries. By Sir C. Lyell, F.R.S., D.C.L. ^c.f 



SINCE the publication in the Philosophical Transactions of 

 my paper on the Lavas of Mount Etna J, a Report by Prof. 

 ' Smyth, Her INIajesty's Astronomer for Scotland, has been printed 

 by the Admiralty of Great Britain, " On the Teneriffe Astrono- 

 mical Experiment of 1856,^' in which a chapter on geology and 

 " volcanic theories" is introduced. 



This chapter, which did not form part of the original Report 

 as published by the Royal Society in the Philosophical Transac- 

 tions lor 1858, contains a discussion of Von Buch's theory of 

 craters of elevation, together with critical remarks on passages 

 in my writings, and those of Mr. Poulett Scrope. I do not feel 

 myself called upon to reply to any of these comments, as they 

 i-elate to subjects to which the Astronomer for Scotland cannot 

 be expected to have devoted much time or attention ; but when 

 facts are cited, respecting Teneriffe and other islands of the 

 Canarian Archipelago, supposed to be conclusive on a contro- 



* I liuvc already described two such spectra, in order to give a prelimi- 

 nary idea of a gas-spectra. The first was shown by a not very narrow 

 hydrogen tube, which was among the first which M. Geissler made. I 

 chose this on account of its simplicity ; but it does not belong to pure hy- 

 drogen, as we now see at a glance. The second beautiful spectrum 

 described, which is mentioned as belonging to fluoride of boron, probably 

 also does not belong to the pure gas. If we consider its less refrangible 

 portion with the narrow grey lines, we may assume with tolerable certainty 

 that the gas contained nitrogen (air) (70), (71). 



t Communicated by the Author. 



X " On the Structure of Lavas which have consolidated on steep slopes j 

 with Remarks on the Mode of Origin of Mount Etna, and on the Theory of 

 ' Craters of Elevation,' " by Sir Charles Lvell, Phil. Trans, part 2, 1858, 

 p. 703 



