Volcanos and Earthquakes. 51 



way onwards, and thus stopped up the channels. If, in this 

 case, water should descend through rents into this btill ex- 

 tremely hot lava, hot springs would also thus be produced, sup- 

 posing a communication between these and other rents which lead 

 to the surface at a lower level ; but these springs will decrease in 

 temperature by degrees as the lava gradually cools, till they 

 reach that degree which naturally belongs to the place where 

 the lava is situated. However, we have already proved by ex- 

 periments formerly mentioned, and calculations founded upon 

 them, that, if such masses of heated lava be of considerable ex- 

 tent, a very long period may elapse before the decrease in the 

 temperature of the springs will be even perceptible.* On the 

 other hand, there are examples of a very rapid decrease in the 

 temperature of hot springs in the neighbourhood of volcanos 

 recently become extinct. Thus, the temperature of the hot 

 springs on Jorullo decreased 40°5 F. in 24 years, between 

 the visits of Von Humboldt and JBurkart.f The tempera- 

 ture of the mixture of gases which issues from the rents in the 

 Pass of Quindiu, near the Moral, in the Quebrada del Azvfral^ 

 decreased from 1801 to 1827, according to the observations of 

 Von Humboldt and Boussingault, from 11<8° to 66°4.J If,. 

 instead of this gas, a mineral spring had flowed at this place, it 

 would, doubtless, have suffered a similar diminution of tempe- 

 rature. Boussingault mentions, on the other hand, that, in a 

 a period of twenty-three years, the temperature of the hot 

 springs of Mariana and Las Trincheras rose several degrees. 

 According to the observations of Hamilton, Delia Torre, 

 Abbe Soulavie, Von Humboldt, and Forbes, the hot spring 

 named La Fisciarella, which rises near Naples, from the exte- 

 rior of the cone of the Solfatara, is subject to extraordinary al- 

 ternations in its temperature, from 101° F. to 199°4 F.§ 

 But even in very short periods striking differences are some- 



* Die vulkanischen Mineralquellen, &.c. p. 150. — I have calculated, 

 that, under the circumstances there mentioned, a mass of melting basalt, 

 equal in size to one-third of the Donnersberg^ near MiUeschaUy in Bohemia, 

 Avould be sufficient to have heated all the water which has issued from 

 the whole number of springs at Caaishad since the time of Adam. 



t Burkart, loco cit. t. i. p. 22C. 



+ Poggendorft's AnnaL t, xviii. p. 858. 



§ Forbes, loco cit. p. Gil. 



