Check out "The Scientific American Book Of Projects For The Amateur Scientist" - C. L. Strong describes quite a bit of this in the section "The earth sciences".

Check out "The Scientific American Book Of Projects For The Amateur Scientist" - C. L. Strong describes quite a bit of this in the section "The earth sciences". The schematics date from 1960 (tubes, not transistors) but you'll find updates around the web. http://www.sciencemadness.org/library/books/projects_for_the_amateur_scientist.pdf http://www.sciencemadness.org/library/books/projects_for_the...