THE AGE OF THE EARTH. 



339 



extend to 250 miles or about 0-OGof radius. Surface r^te appears both 

 in ° F. and feet, and '^ C and meters. Tables .> and 4 exhibit similar 

 data for earths of lower initial excess and shorter periods of secular 

 cooling. Table 3 is computed for an earth of 1,740° C, -{OxlO" secular 

 cooling, and table 4 for 1,230'^ C, lOx 10" cooling. 



Taisle N'o. I. — Estimated varth pressures {Laplace's deitsU'ms), it heiiii/ radial distances 

 from the center of the earth and p l)vin(j the pressure corrcspondinfj to n expressed in 

 atmospheres. 



Table No. 2. — Estimated earth temperatures. Initial excess of 3,900^ C. 100,000,000 

 years' secular cooliuf/ with surface rate of 1^ F. for 506 feet of depth. Thermal conduc- 

 tion 400 feet^ /year {Lord Kelvin's case. 



Table No. 3. — Estimated earth temperatures Initial excess 1,741- C. {about melting 

 point of platinum) 30,000,000 years' secular cooliny with surface rate of 1"^ F. to 50' 6 

 feet of depth. Thermal conduction 400 feet- /year. 



