570 Reviews — Prof. Tschermak — On Vo/canic Action. 
to owe their shapes to eniptions. The sunspots are emptions of 
incandescent gas : the sudden brilliancy of some stars points to a 
sirailar cause. The forms and inaterials of xneteorites may be due to 
ejection from some planet in volcanic activity, perhaps now itself 
reduced to fragments. He will consider whick of the many kypo- 
theses brought forward will bear application to the earth and 
extension to the universe. First he describes the theory which 
attributes volcanic pkenomena 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 ougkt 
either to be continuous or regularly periodic, also that it fails to 
explain the origin of many products of eruptions, especially carbonic 
acid gas, nitrogen, ammonia, sulphürous and sulphuric acids, etc., 
and that the moon skows 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 Roth, and 
it öfters no explanation of the Chemical products. He briefly dis- 
misses the Suggestion of Nasmyth and Carpenter, that the moon’s 
materials expnnd in solidifying; as also that of Davy that the earth's 
interior contains potassium. 
He then enunciates bis own hypothesis, first developed by Angelot 
in 1842, that the molten materials witkin 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 kimseif 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 bekaviour. Especially he urges the agree- 
ment of bis theory with the hypothesis of Kant and Laplace — the 
origin of all keavenly bodies by condensation of gases. In their 
solidi fication these bodies would include quantities of the simple 
gases. which at those temperatures would be elements, but when 
disengaged in cooling migbt 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 irregulär 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 
