Interior of the Globe, 35 



extremely elastic substance, such as elemental fire or light. 

 In these calculations, the modifying effects of heat were loft 

 out of view ; and partly, perhaps, on this account, partly from 

 the insufficiency of the data, no great importance seems to 

 have been attached to the result by men of science. So far as 

 I can see, Mr Hopkins's conclusions would only be partially 

 affected by a more accurate determination of the relations 

 between pressure, density, fusibility, and heat. Such deter- 

 mination would merely add a little to, or subtract a little 

 from, the thickness of the crust, which must still remain a large 

 submultiple of the radius. 



From the rapid increase of heat as we descend beneath the 

 surface, it had been inferred that a temperature sufficient to 

 fuse every known substance, would be found at a very mode- 

 rate depth. Cordier, one of the first who took a comprehen- 

 sive and scientific view of the subject, thought that the thick- 

 ness of the crust did not probably exceed sixty miles, but 

 might be much less ; and he further inferred that the lavas 

 flowing from volcanoes were merely portions of the great central 

 reservoir of molten matter, squeezed out in consequence of a 

 slow contraction of the shell of the globe, produced by secular 

 refrigeration.* Like Mr Leslie, he made no allowance for the 

 antagonism betwixt heat and pressure. It was justly objected, 

 too, that the supposition of the depth of the solid envelope 

 being so small — only one-sixty-sixth part of the semi-diameter 

 — in comparison with that of the fluid mass within, was incon- 

 sistent with the known stability of the earth's surface. 



Mr Hopkins's conclusion, no doubt, rests on a narrow enough 

 basis. It is something like an estimate of the distance of the 

 stars, deduced from a difference of one or two seconds in their 

 apparent position — a difference scarcely distinguishable from 

 errors of observation — but in the absence of more direct and 

 positive evidence, we are thankful to obtain it. I beUeve it 

 to be correct in principle, and that its errors, if any, are errors 

 of degree ; and the views respecting the structure of the globe, 



♦ Essai 8ur la Temperature de rinterieur de la Terre ; lu a I'Aca- 

 demie des Sciences, Juin 1827. His estimate is 20 leagues of 5000 

 metres. 



