PAPERS PRESENTED AT GENERAL SESSIONS 61 



From an astronomical point of view the earth is a small 

 body although it is the largest solid body with which we 

 are acqnainted. It seems to be near a border line. Plan- 

 ets and satellites smaller than the earth seem to be solid 

 like the earth itself, and of smaller density, while bodies 

 larger than the earth are largely if not wholly gaseous. 

 From the point of view of pressure this would seem to 

 indicate that the pressure at the center of the earth is 

 approaching a critical pressure beyond which a solid or 

 liquid state cannot exist. In other words a solid or liquid 

 body much larger than the earth, and composed of the 

 same substances, cannot exist on account of the great 

 pressures developed in the interior. It is not reasonable 

 to suppose that any organized structure, and the atom is 

 known to be such, can withstand an unlimited amount of 

 violence. We are not at liberty therefore to suppose that 

 solid or liquid bodies can increase indefinitely in size, for 

 the pressure at the center goes up faster than the square 

 of the radius. Just what that maximum size would be we 

 could not tell from any laboratory experiments on matter, 

 but we can examine the various astronomical bodies in the 

 solar system and this examination suggests that the 

 earth is not far from the maximum size. The mass of 

 Uranus is 14.4 times the mass of the earth and Neptune is 

 16.7 times the mass of the earth. If they were of the same 

 density as the earth their diameters would be two and 

 one-half times the diameter of the earth and pressures 

 would rise to twenty millions of atmospheres. Actually, 

 they are not solid bodies, for their densities are 1.44 and 

 1.09 respectively as compared with 5.5 for the earth. It 

 will be observed that Xeptune is slightly more massive 

 and slightly less dense than Uranus. These facts imply 

 that the mass of Uranus is greater than the maximum 

 solid mass and consequently a large proportion of its 

 mass is in the gaseous state. Xeptune is slightly farther 

 from the maximum point and a greater proportion of its 

 mass is gaseous since its density is smaller. 



Saturn is the next larger body with a mass 94 times 

 that of the earth. If it were as dense as the earth its di- 

 ameter would be 4.5 times that of the earth and its cen- 

 tral pressure would be about 75 millions of atmospheres. 



