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…of the Sun. Therefore subterraneous fire was necessary in the internal Oeconomy, or constitution of, as it were, the organiz’d parts of the earth, and distribution of Life and heat, as we may so say, to all the exteriour members. Plato acknowledges hidden treasuries of ever flowing flames, and most huge Rivers of fires, as well as of waters. Yea and…
https://www.wichita.edu/academics/fairmount_las/geology/wparcell/Kircher/volcanoes/chapter1.php