﻿570 Revieios — Prof. Tschermak — On Volcanic Action. 



to owe their shapes to eruptions. The sunspots are eruptions of 

 incandescent gas : the sudden brilliancy of some stars points to a 

 similar cause. The forms and materials of meteorites may be due to 

 ejection from some planet in volcanic activity, perhaps now itself 

 reduced to fragments. He will consider which of the many hypo- 

 theses brought forward will bear application to the earth and 

 extension to the universe. First he describes the theory which 

 attributes volcanic phenomena to the mutual action of the water 

 which percolates down and the heated rock which it meets. This 

 explains many of the circumstances. He objects to it, however, 

 that since percolation is a continuous process, volcanic activity ought 

 either to be continuous or regularlj'^ periodic, also that it fails to 

 explain the origin of many products of eruptions, especially carbonic 

 acid gas, nitrogen, ammonia, sulphurous and sulphuric acids, etc., 

 and that the moon shows numerous volcanos but no water. 



Next he describes Mallet's suggestion that the heat is owing to 

 the sinking of portions of the earth's crust into cavities produced by 

 contraction. This he says could not develope a temperature nearly 

 sufficient ; its weakness has been shown by 0. Fisher and Eoth, and 

 it offers no explanation of the chemical products. He briefly dis- 

 misses the suggestion of Nasmj'th and Carpenter, that the moon's 

 materials expand in solidifying ; as also that of Davy that the earth's 

 interior contains potassium. 



He then enunciates his own hypothesis, first developed by Angelot 

 in 1842, that the molten materials within the earth contain absorbed 

 in them quantities of vapours or gases, which, in solidifying, they 

 disengage. Angelot thought this would not account for the amount 

 of action, but he himself considers that he has calculated that it will. 

 The irregularity of eruptions he attributes to the irregularities in the 

 interior. He adduces the quantities of gases found contained in me- 

 teorites. He explains on this hypothesis the disengagement of gases 

 from lava, its origin, and its behaviour. Especially he urges the agree- 

 ment of his theory with the hypothesis of Kaat and Laplace — the 

 origin of all heavenly bodies by condensation of gases. In their 

 solidification these bodies would include quantities of the simple 

 gases, which at those temperatures would be elements, but when 

 disengaged in cooling might meet, combine, and so produce great 

 and sudden developments of heat. The application to solar eruptions 

 is plain. If small bodies were so formed, their quicker cooling 

 might cause explosive action more violent than ordinary, resulting 

 in swarms of irregular fragments, and perhaps the complete destruc- 

 tion of the bodies. Thus he accounts for meteorites. The small 

 attraction of such bodies would be insufficient to retain water un- 

 vapourised on them. Now meteorites, he says, contain generally 

 anhydrous minerals. If the moon be derived from a former ring 

 (like one of Saturn's) round the earth, its materials would be light. 

 If its surface consist of light absorbent materials, these may retain 

 the steam and gases disengaged from the interior, and account 

 for the absence of a visible atmosphere. 



In Appendix I. (pp. 18-20) the author estimates the degree of 



