Nature of the Earth's Interior. 167 



Himalayas of Asia, or the Andes of America, whicla are, as it were, 

 masses of heavy matter piled up high above its mean surface-level. 

 At first sight this style of reasoning not only appears plausible, but 

 even seems threatening to upset the entire hypothesis altogether ; it 

 requires, however, but little serious consideration to prove it to be 

 more, so to say, sensational than actually founded upon the facts of 

 the case ; since it is only requisite for us to be able to form in our 

 mind some tangible idea as to the relative proportions which the size 

 of even the highest mountain bears to that of the entire globe, to 

 convince us thoroughly, that if such a crust could once form and sup- 

 port itself, that it could with ease support the weight of the mountains 

 also. This will be at once seen by a glance at the diagram before 

 you, which represents, upon a scale of 200 miles to the inch, an 

 imaginary section through the centre of the earth, whose mean dia- 

 meter is taken at 7912 miles. The thickness of the earth's crust, 

 supposing it to be, as before estimated, about 50 miles, is on this scale 

 denoted by the black outer line or zone, only a |- of an inch in width, 

 whilst on the top of this again are placed (coloured bright red) some 

 little markings, scarcely amounting to more than a slight roughness 

 on the outline of the circle, and which is quite impossible for any one 

 to see, except upon very close inspection, since they at the highest 

 part do not project more than -J^. of an inch above the circle itself; 

 these markings, however, do upon this scale represent the actual 

 comparative size of the great Himalaya chain of mountains, which 

 rise to a maximum altitude of 31,860 feet, or six miles above the 

 mean level of the sea. From this it will be readily perceived that 

 if the earth could be seen reduced in scale down to about the size of 

 an orange, that to all practical intents and purposes it would resemble 

 to the eye an almost smooth ball, since even the highest mountains 

 and deepest valleys upon its surface would not present to the eye 

 greater inequalities in outline than the little pimples and hollows on 

 the outside of the skin of an ordinary orange. A mere glance at such 

 a diagram will therefore, I think, fully convince us that if this thin 

 crust can support itself, it is not at all likely to be crushed in by the 

 comparatively speaking insignificant weight of even our very highest 

 mountain chains ; in fact it would be quite as unreasonable to maintain 

 such a supposition as to declare that the shell of a hen's Qgg would 

 be crushed in by simply laying a peice of a similar eggshell upon its 

 outside. 



That a very thin spheroidal crust or shell, inclosing a body of 

 liquid matter, such as an ordinary fowl's egg, does possess in itself 

 an enormous degree of stability, and power to sustain pressure from 

 without, is easily demonstrated experimentally, by merely loading a 

 small portion of its surface with weights, as long as it does not give 

 way under them. Even when placed upon its side (or least strong 

 position), it was found that a portion of the shell of a fowl's egg, 

 only one quarter of an inch square, could sustain several pounds' 

 weight, without showing any symptoms of either cracking or crush- 

 ing, or, in other words, this simple experiment indicates that if the 

 external crust of the earth was only but as thick and strong in pro- 



