92 Professor A. E. H. Love [March 6, 



WEEKLY EVENING MEETING, 



Friday, March 6, 1908. 



Donald W. C. Hood, Esq., C.V.O. M.D. F.R.C.P., Vice-President, 



in the Chair. 



Professor A. E. H. Love, M.A. D.Sc. F.R.S. 



The Figure and Constitution of the Earth. 



The subject of this lecture is the figure and constitution of the Earth. 

 I have chosen this title in order to draw attention to the theory which 

 asserts that the shape of the earth is an outward and visible sign of 

 its inward structure. We know that the shape of the earth is a very 

 good sphere. It would be difficult to make so exact a sphere. If 

 we could make a model 25 feet in diameter the inequality of the 

 surface would have to amount to no more than one inch. That is to 

 say, the longest diameter of the model would have to exceed the 

 shortest by one inch. Tlie inequalities of the surface, trifling as 

 they are in comparison with the dimensions of the earth, are very 

 important to mankind, and we try to understand how they came to 

 be what they are. 



The greatest interest attaches to those inequalities which are con- 

 cerned in the distribution of continent and ocean ; but, before passing 

 to the consideration of these, I must advert to that inequality which, 

 although it is the greatest of all, has hardly any influence upon this 

 distribution. A rotating body of planetary dimensions cannot be a 

 perfect sphere ; but, owing to the rotation, the equatorial parts must 

 be driven outwards from the axis, and the formation of the equatorial 

 protuberance must be compensated by the flattening of the parts near 

 the axis. Newton determined the shape as an oUate spheroid, the 

 figure formed by the revolution of an ellipse about its shortest 

 diameter. The relative situation of an oblate spheroid of small 

 ellipticity and a sphere of equal volume may be illustrated by an 

 ellipse and a concentric circle, adjusted so that the diameter of the 

 circle exceeds the shortest diameter of the ellipse by twice as much as 

 the longest diameter of the ellipse exceeds the diameter of the circle. 

 [The figure was sliown on a lantern slide.] In the case of the earth, 

 the elevation all round the equator is about 4^ miles, the depression 

 at either pole about 8f miles. The result that there is equatorial 

 protuberance as well as polar flattening, and that the one is half as 

 great as the other, is as much a part of the theory, and is as well 



