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and I am ready to take five-and-a-half times as the average density 

 of the earth, including every part of it. The consequences which 

 flow from that are rather striking. Of course, as this density is 

 much more than double that of the surface, it shows that it is 

 more dense towards the centre than the outside. One result of 

 the calculation rather startled me when I made it. Since the 

 constituent parts of the earth press upon one another as you go 

 down, what is the pressure per square inch when you approach 

 the centre of the earth 1 There are many gentlemen among you 

 who have heard of a pressure of fifty or a hundred or two hundred 

 or three hundred pounds on the square inch. I believe the 

 greatest we know is ten thousand pounds on a square inch of 

 tough Aberdeen granite, which is just sufficient to crush the 

 granite. My calculation of the pressure at the centre of the earth 

 gave thirty millions of pounds on every square inch. It is an 

 astounding thing, and we cannot conceive what consequences may 

 follow on that. The word million runs very easily off the tongue, 

 but if you attempt to construct it you find it a very unmanageable 

 thing. If you make a hundred dots on a page, and do the same 

 over ten thousand pages, you will find it will take a long time to 

 make those dots ; and if you repeat it thirty times, you will 

 find it an enormous labour for which life will hardly suffice. But 

 to conceive that as the pressure of things at the earth's centre — 

 we don't know such a thing ; we don't know the consequences. 

 Perhaps gas maybe squeezed into gold, or silver into platinum j 

 a solid may be forced into powddr, or powder into a solid. We 

 are in total ignorance ; and that is one of the troubles of this 

 case. 



Now I come to a result of another kind, namely, that of the 

 rotation of the earth. The earth revolves once in the course of 

 a day. Everybody knows also, from the housemaid who spins a 

 mop to the highest philosopher, that the rotation would swell out 

 the middle of the earth. Calculations have been made on that, 

 and the result is that the diameter of the earth in the equatorial 

 direction is greater by about one three-hundreth part than the 

 diameter in the polar direction. I cannot attempt to represent 



