FWIW, #4 "Two 4000 ft plumb bobs hung down a mine shaft, with baffling results (1901)" can be found at http://www.lockhaven.edu/~dsimanek/hollow/tamarack.htm ht

FWIW, #4 "Two 4000 ft plumb bobs hung down a mine shaft, with baffling results (1901)" can be found at http://www.lockhaven.edu/~dsimanek/hollow/tamarack.htm http://www.lockhaven.edu/~dsimanek/hollow/tamarack.htm