134 Proceedings of the Royal Physical Society. 



of which the crust is composed contract uniformly by dimi- 

 nution of temperature, and at the rate of j^?* for every 

 180° Fahr., which is the rate of contraction of flint glass. 

 Then we have 180° : T ^ : : 1500 : F f|- ¥ = T *J T¥ , and 

 Tii-rv °f 45000 yards (taking this as the thickness of the 

 crust) == 30048 yards, the amount which the radius would 

 be shortened by a loss of 3000° of surface temperature. The 

 circumference of the earth would thus be reduced by 30048 

 x 34416 x 2 = 1886-976 yards,f so that a point on the 

 surface at the equator would have its diurnal orbit lessened 

 to this extent. Since the space moved over by the crust in 

 its daily axial revolution would thus be diminished, whilst 

 its momentum continued the same as before, a shortening 

 of the day to a certain amount would necessarily take place. 

 Suppose now the original diurnal period of the earth to have 

 been 24 hours, then 43,781,760 yards (or 24,876 miles, being 

 the circumference of the earth) : 1887 yards : : 86164* (24 

 hours) : 3"'7136, which would be the amount of the daily 

 acceleration of the crust, but for the retarding influence of 

 the friction of its lower surface upon the molten interior. 



5. The loss of heat at the surface being assumed = 3000°, 

 the corresponding contraction will be T i-8 8> ari d. the super- 

 ficial contraction of a great circle of the earth = 2 4 8 7 6 : or 



° 7 4'8 8 ' 



say g 6oo o _ 3331 miles, which would be the aggregate 

 width of the fissures opened on the whole circumference 

 of the earth by a reduction of temperature to this amount. 

 This is equivalent to 195 \ yards for every degree of 

 Fahrenheit. 



6. By this refrigeration of the crust, and the consequent 

 contraction of all its parts, its capacity would obviously be 

 diminished, so that it would grasp the internal molten mass 

 with greater and greater force, until the tension became. ex- 

 treme, when Assuring would ensue and molten matter would 

 be erupted, until the capacity of the crust and the quantity of 



* According to the very careful experiments of Mr Adie, the contraction of 

 a column of Eatho greenstone cooled 1000° was 4| per 1000. For 180° this 

 would amount to is^Veysr* or a little exceeding that of flint glass, so that 

 the rate above assumed is perhaps not very far from the truth. 



t Or 1-2578 yards for each degree of Fahrenheit. 



