240 POPULAR SCIENCE MONTHLY. 



structures underlying psycliological processes will be found to 

 account for the presence of the extraordinary talents of idiots 

 savants. It is questionable whether Heinecken, the " child of 

 Ltibeck/' should be included among any of the cases described 

 here. He died too soon (at the age of four years) for the fact of 

 mental weakness of any kind to be established ; but his precocity 

 made him the wonder of his time (1731-'25). He knew the chief 

 incidents of the Pentateuch at the age of one year, had mastered 

 all of sacred history at two years, and was intimately acquainted 

 with modern and profane history and geography, and spoke 

 French and Latin, besides his native tongue, at the age of three. 

 Surely such precocity as this must have been due to extraordi- 

 nary aggregations of gray matter in parts of the brain of a truly 

 abnormal character. 



IGNEOUS INTRUSIONS AND VOLCANOES. 



By ISEAEL C. KUSSELL, 

 professor of aeology in the ukiveksity of michigan. 



MANY geologists have watched the action of volcanoes in 

 eruption, and have gazed into their craters when in a state 

 of mild activity. One of the most striking of the phenomena 

 revealed at such times is that great volumes of steam are given 

 off from the molten lava which rises in the craters. This steam 

 either escapes quietly, as in the case of the Hawaiian volcanoes, 

 or with explosive violence, as in erux)tions of the Vesuvian type. 

 It is now conceded by probably all students of volcanoes that the 

 proximate cause of the violent explosions accompanying many 

 volcanic eruptions is the sudden escape of highly heated steam. 

 Most modern theories advanced to account for volcanic phenom- 

 ena are based on the assumption that steam is the propelling force 

 which causes the lava to rise from deeply seated sources and to be 

 extruded at the surface. Steam contained in the molten lava is 

 thought by Shaler and others to cause the molten rock to rise and 

 overflow, in much the same way that carbonic acid generated in 

 dough causes it to expand, or as the carbonic acid in ale makes it 

 overflow when the cork of a bottle in which it is contained is with- 

 drawn. In these theories, heat is considered as the prime souroe 

 of energy, and that, given the heat, steam will be generated which 

 will force the lava to the surface. 



I do not wish to criticise the theories that have been advanced, 

 or even to attempt to review them, but simply to change the point 

 of view from which volcanoes have commonly been studied, in 

 the hope that the phenomena observed will group themselves in 

 another and perhaps more instructive way. Current theories are 



