THE TIDAL WAVE ON THE OFF SIDE OF THE EARTH. 181 



points of the surface where it will yield, while causing the 

 intermediate areas to bulge out from the normal form ; and that 

 this is the case can be shown from a consideration of the 

 moon's action on the side of the earth immediately opposed 

 to it. 



If we draw a line from the centre of the moon to that of the 

 earth we have the position of maximum attraction between the 

 two bodies ; but the attraction of the moon extends over the 

 w hole of the side of the globe presented to it. 



Proposed Solution of the Problem. — Assuming the earth to 

 consist of a solid, but flexible, envelope of a minimum thickness 

 of 28 miles, but which owing to gravitation may be twice this 

 amount, enclosing a molten or viscous mass of matter due to 

 primeval heat, and revolving on an axis with a velocity of a 

 thousand miles an hour at the equator. 



The effect of attraction of the moon on the globe will be 

 greatest in a line joining the centre of the former with that of 

 the latter — a distance of 240,000 miles — and whatever may be 

 its force at the surface of the earth directly opposite to it along 

 this line it will be less at the centre of the globe, according 

 to the Newtonian law of " inversely as the square of the 

 distance." Both the moon and the globe are mutually attract- 

 ing each other ; but as the latter is much larger than the 

 former the centre of gravity of the joint system will not be the 

 centre of the globe, but in a position between the centre and 

 edge of the globe itself. This is of little consequence to my 

 argument. According to the Newtonian law, the attractive 

 force of the moon will be decreased at the off side of the globe 

 as compared with that at the centre, and the attraction at the 

 centre again will be less than at the surface immediately under 

 the moon. But, beside the force of the moon's attraction on 

 that part of the globe directly opposite to itself, its force is 

 spread over the entire hemisphere, decreasing with the distance 

 from the central axis in all directions towards the great circle 

 which has the moon at its pole. At that circle a portion of 

 the moon's attraction acts as a lateral pressure directed from 

 opposite sides towards the centre of the earth. It is this 

 lateral pressure which (as I contend) produces the second (or 

 antipodal) bulging, resulting in the tidal wave on the off side of 

 the globe from the moon. 



This lateral pressure affects the whole mass of the globe, and 

 necessarily produces a bulging of the surface over the region 

 intermediate between the regions of pressure. As the whole of 

 the interior mass which I infer, on grounds already stated, to 



