1869.] TJie Artificial Production of Ice and Cold. 197 



M. Delaimay has, however, clearly shown that "there is a 

 fundamental error — not in the mathematical formula, but in the 

 condition assumed, namely, that the interior is filled with a free- 

 flowing liquid rock." 



" The interior fluid can only be of the nature of lava, and that, 

 when examined at the surface, however fresh, is a very intractable 

 mass, flowing indeed as does thick honey, pitch, or slag ; incapable 

 of moving at the very utmost above a few miles an hour even on a 

 slope of 30^, and on ordinary slopes only one mile, half-a-mile, or 

 even thirty or forty feet in an hour. The problem solved by Mr. 

 Hopkins, looked at in this hght, does really not settle anything as 

 to the thickness of the crust of the earth." 



" The globe is continually, though very slowly, losing heat ; it 

 grows cooler in a very small degree, and sufiers contraction in the 

 same small degree." . . . "From what we certainly know of the 

 constitution of the crust of the globe, it is of unequal strength to 

 resist change of form in diflerent parts. The weakest part must 

 yield, and if by local yielding the general pressure may be satisfied 

 (which is equivalent to supposing the general pressure determined 

 to a small area), the displacement of a small tract may be extremely 

 great, and the rocks there be bent into arches or broken by faults. 

 If we are right in our views of the history of the globe, very many 

 epochs would arise, when, first in one region, then in another, lines 

 or areas of relative weakness would be depressed into concave seas, 

 and receive a long series of deposits ; and at other times the same 

 areas or parts of them might be re-elevated, producing end-pressures 

 and violent local flexures or fractures." 



With these extracts from Chapter XII. of Professor Phillips's 

 book we must now conclude this brief sketch of Vesuvius, hoping 

 some day to be able to look at the probable connection between 

 lines of volcanoes and volcanic centres and old volcanic areas now 

 extinct, in other parts of the world. 



IV. THE AKTIFICIAL PEODUCTION OF ICE 

 AND COLD. 



By Dr. B. H. Paul. 



The application of heat for cooking food has been considered one 

 of the most obvious characteristics by which man is distinguished 

 from the lower animals, and there is even still greater reason for 

 regarding the application of this physical agency for various 

 economic and industrial purposes, as being one of the circum- 

 stances most important in determining the difference between 



VOL. VI. P 



