356 Mr Fisher, On the transmission of 



And by Henry's law the volume absorbed is constant, and = rV. 



P 

 ..". volume of free gas + rV= •— rV; 



P 



. • . volume of free gas = r V I 1 J . 



We may suppose that the magma as a liquid is subject to 

 voluminal expansion from V to V owing to the change of P to p ; 

 and let e be the coefficient of voluminal compression at the 

 pressure P. 



Then e = increment of pressure -r- voluminal compression 



V'-V 



v 



Whence V = 



e 



Hence, supposing if possible the magma to expand and gas to 

 be simultaneously extruded, we should have for the total expanded 

 volume at the pressure p, 



volume of free gas + volume of expanded magma 



=rF (£_ 1 ) + _^_. 



1- 



e 



Therefore putting Bsc for V, we should have, 



MN \p J x P-p da:' 



e 

 -pdp 1 dp 



dec e doc _ d?% 



p 2 ( P — pY dx 2 ' 



1- 



e 



N ow p — p is the relaxation of pressure which causes the 

 disturbance. It is obvious that this must be small compared 

 with P, for P being the pressure of the crust, if P—p was equal 

 to P it would imply that the crust was entirely removed above 

 the area of disturbance. 



P—p 



Let then — p-- = a, where a is small. 



p dp d£ 



dx r dx r dp lA , , , 



