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A New Theory of (he Central Heat of the Earth, and of the 

 cause of Volcanic Phenomena. By Mr Stevenson Mac- 

 adam, Teacher of Chemistry, Philosophical Institution, 

 Edinburgh. Communicated by the Author.* 



The projection of matter in a fused state from the craters of 

 volcanoes, and the emission of hot water from certain springs, 

 led philosophers, in early times, to suppose that a high tem- 

 perature prevailed in the lower regions of the earth. This 

 has been latterly distinguished as the " central heat" of the 

 globe. In later years this opinion has been strengthened by 

 the rapid increase in temperature observed to be exhibited 

 by the constituents of the earth's crust, as we descend from 

 the superficial to the lower strata. This augmentation in 

 temperature has been ascertained, by thermometrical obser- 

 vations made in deep mines, wells, &c., to be such that, 

 according to Cordier, it is not overstated at 1° F. for every 

 forty-five feet of depth. 



The observations on this increase, although they extend to 

 a comparatively insignificant depth in the terrestrial crust, 

 furnish data by which, provided we assume that the increase 

 in temperature is at the same rate, at great as at small 

 depths, we may calculate the temperature at any distance 

 from the surface. Certain geologists, accordingly, calculating 

 in this way, have come to the conclusion that the intensity 

 of heat of the central nucleus will not be less than 450,000° F. 

 Others, again, placing a limit to this rise of temperature at a 

 certain depth, are of opinion that a cessation of this increase 

 occurs there, and that all matter placed betwixt that point 

 and the centre of the globe is possessed of an uniform tem- 

 perature. 



The advocates of the theory which supposes that the heat 

 continues to increase to the centre of the globe, assume the 

 possibility of a crust of solid matter, at a comparatively low 

 temperature, enclosing a mass of liquid at a very high tem- 

 perature ; whilst the thickness of this crust bears the same 



* This Memoir, in a more extended form, was laid before the meeting of the 

 British Association at Edinburgh, 1860. 



