142 Fisher — Notes to Rival Theories of Cosmogony. 



(4) The lava issued from Etna at 1932° Fah. We can find 

 the depth at which that temperature would have been pro- 

 duced by compression of surface rock. 



We have 



temperature Fah. = — - — — 

 Jcr p 



Applying this to the present case, we get 



(p-»)'_ 



5:043 x 10 = 2m, suppose, 



whence 



± V (s 4- m)' 



Since the surd is greater than m and (p — s) must be posi- 

 tive, we must use the upper sign ; we then obtain 



p — s = 0-120. 



This will be the increase of density to the depth where the 

 temperature is 1932° Fah. or p = 2*87. 



We then require the value of r which will make 



sin^- = 2 . 87 



r 



It appears on trial that a depth a — r of about 40 miles satis- 

 fies this condition. It follows that the depth at which the 

 temperature 1932° Fah. would be produced would be about 40 

 miles. 



Table. 



Tenths 



Approximate 



depth in 



miles. 



Densities 



by 



Laplace's 



Law. 



Pressure in 

 atmospheres. 



Condensation 



von i n^itp rn 



of 

 radius. 



J LUUIOllv l-\J 



Vo 



reduce surface 











rock to density. 



1-0 







2-75 



o-ooo 



o-ooo 



0-9 



^400 



3-88 



2-181 X 10 7 



0-29 



0-8 



800 



5-03 



5-055 X 10 7 



0-45 



0-1 



1200 



6-17 



8-460 X 10 7 



0-55 



0-6 



1600 



7-25 



12-344 X 10 7 



62 



0-5 



2000 



8-23 



16-867 X 10 7 



0-67 



0-4 



2400 



9-09 



20-698 X 10 7 



0-70 



0-3 



2800 



9-80 



24-370 X 10 7 



0-72 



0-2 



3200 



10*32 



27-030 X 10 7 



0-73 



o-i 



3600 



10-64 



29-052 X 10 7 



0-741 



o-o 



4000 



10-74 



30-061 X 10 7 



0-744 



