.3:28 Mr. 11. Mullet on Volcanic Entry!/. [May 7, 



some 4000 or 5000 feet into the mountains, when, in these latitudes at 

 least, the reflecting surface must necessarily be snow. 



In the above remarks I have confined myself strictly to the physical 

 aspect of the subject ; but it is obvious that, in seeking an alpine sani- 

 tarium, the patient comes under new conditions of respiration, and 

 breathes air comparatively free from zymotic matter circumstances 

 which are probably not without profound influence upon his health. 



III. Addition to the Paper, " Volcanic Energy : an attempt to 

 develop its true Origin and Cosmical Relations " *. By 

 ROBERT MALLET, A.M., C.E., F.R.S., M.R.I.A., &c. Re- 

 ceived April 3, 1874. 



(Abstract.) 



Referring to his original paper (Phil. Trans. 1873), the author re- 

 marks here that, upon the basis of the heat annually dissipated from our 

 globe being equal to that evolved by the melting of 777 cubic miles of 

 ice at zero to water at the same temperature, and of the experimental 

 data contained in his paper, he had demonstrated, in terms of mean 

 crushed rock, the annual supply of heat derivable from the transforma- 

 tion of the mechanical work of contraction available for volcanic energy, 

 and had also estimated the proportion of that amount of heat necessary 

 to support the annual vulcanicity now active on our globe ; but, from the 

 want of necessary data, he had refrained from making any calculation as 

 to what amount in volume of the solid shell of our earth must be crushed 

 annually, in order to admit of the shell following down after the more 

 rapidly contracting nucleus. This calculation he now makes upon the 

 basis of certain allowable suppositions, where the want of data requires 

 such to be made, and for assumed thicknesses of solid shell of 100, 200, 

 400, and 800 miles respectively. 



From [the curve of total contraction (plate x. Phil. Trans, part i. 

 1873) obtained by his experiments on the contraction of slags, he has 

 now deduced partial mean coefficients of contraction for a reduction in 

 temperature of 1 Fahr.,for intervals generally of about 500 for the entire 

 scale, between a temperature somewhat exceeding that of the blast- 

 furnace and that of the atmosphere, or 53 Fahr. And applying the 

 higher of these coefficients to the data of his former paper, and to the 

 suppositions* of the present, he has obtained the absolute contraction in 

 volume of the nuclei appertaining to the respective thicknesses of solid 

 shell above stated. In order that the shell may follow down and remain 

 in contact with the contracted nucleus, either its thickness must be in- 



* Eead Juno 20, 1872 ; IMiil, Trans, for 187'% p. 147. 



