Royal Institution, 5S5 



depth equal to the height of Snowdon, 3571 feet, upon the average 

 assumed, a temperature of 71" only would be found; at two miles* 

 depth, only the temperature at which water boils at the earth's sur- 

 face under ordinary pressure, or 212° ; and a depth of 30,600 feet, 

 about 5^ miles, (considerably more than equal to the elevation of the 

 highest peak of the Himalayas) must be attained, before we arrive at 

 a temperature adequate to the fusion of lead, or 612° ; whereas the 

 fusion of some of the most refractory earthy substances would be 

 required for the production of volcanic phaenomena. At the depth of 

 about 26 miles, however, which is less than T-J-irth of the earth's 

 radius, a temperature sufficient for the fusion of cast iron would 

 occur (which would of itself be sufficient also for that of many 

 earthy and alkaline compounds) ; at little more than 33 miles deep 

 would be attained the greatest heat of a ffint- glass furnace ; at 37 

 miles soft iron would melt * ; at 50 miles, a temperature of above 

 5000° Fahr. would be obtained, and at 100 miles, only ^'„th of the 

 earth's radius, one of nearly 1 1 ,000°, either of which, from all ana- 

 logy, would be more than adequate to the effects required. If the 

 immense activity generated by such heats may be admitted to take 

 place at these depths, there will be no difficulty in conceiving its 

 extension upwards to depths less great, and finally to the surface of 

 the earth. 



The second part of the subject was commenced by a statement 

 of the chemical theory of volcanos, as originally announced by Sir 

 Humphry Davy, in the Phil. Trans, for 1808, and afterwards re- 

 peatedly advocated ; admitted by him, even when he finally rehn- 

 quished it in favour of the theory of an ignited nucleus of the earth, 

 to be adequate to the explanation of all the phsenomena ; and sub- 

 sequently adopted and expounded in greater detail by Dr. Daubeny. 

 The inference was then draw^n, that if the theory of volcanos depend- 

 ent on that of the secular variation of the isothermal surfaces were 

 true, (and on this point a strong affirmative opinion was expressed) 

 then the chemical theory must also be true, as being necessarily in- 

 volved in the former. This was argued principally on the following 

 grounds : the new deposits formed at the bottom of the sea by de- 

 trital matter must inevitably contain much carbonaceous and other 

 combustible materials derived from organized beings, and these would 

 become distributed, sometimes in a finely-divided state, intimately 

 mingled with earthy bodies, — that is, with the oxides of the earthy, 

 alkaline, and common metals. At the exalted temperatures implied 

 in the theory, many of these oxides, including those of the earthy 

 and alkaline bases, would become reduced to the metallic state ; the 

 ignited water with which the whole would of necessity be saturated, 

 would be decomposed ; its oxygen re-oxidizing the bases, and its hy- 

 drogen being evolved in an uncombined state. Now one of the 

 most abundant elements of all the detrital matter would necessa- 



* As the expressions of many of these high temperatures in degrees of 

 Fahrenheit difTered from the estimates commonly stated, it may be well 

 to add that they were obtained from the experimental resuhs of Wedg- 

 wood, Prinsep, Prof. Daniel!, and others, all having been corrected agree- 

 ably to the pyrometrical researches of the chemist last named. 



