. Annual report of the Board of Regents of the Smithsonian Institution . Based on RaimoncJi& f^ B^ George I Adams. OUR PRESENT KNOWLEDGE OF THE EARTH. By E. WlECHERT,^ Professor of Geophysics at the University of Gottingen. The exiDlorer of nature is naturally inclined to direct his search tothe earth itself, on whose surface we live. He asks what secrets may-lie hidden in the depths beneath our feet. My purpose on the pres-ent occasion is to set forth some of the answers which science is nowable to give to that question. The simplest method, of course, would be for the explorer himselfto pene
. Annual report of the Board of Regents of the Smithsonian Institution . Based on RaimoncJi& f^ B^ George I Adams. OUR PRESENT KNOWLEDGE OF THE EARTH. By E. WlECHERT,^ Professor of Geophysics at the University of Gottingen. The exiDlorer of nature is naturally inclined to direct his search tothe earth itself, on whose surface we live. He asks what secrets may-lie hidden in the depths beneath our feet. My purpose on the pres-ent occasion is to set forth some of the answers which science is nowable to give to that question. The simplest method, of course, would be for the explorer himselfto penetrate into the earth by the way pointed out by the miner. Butthis hope quickly vanishes as we survey the means at our disposaland the results thus far achieved. Mining operations extend to adepth of about 1 kilometer (3,280 feet) ; the deepest shaft ever boredreached a depth of about 2 kilometers (6,560 feet), and the centerof the earth is 6,370 kilometers (about 4,000 miles) beneath us. Wliat are 2 kilometers compared to that? Imagine the earth rep-resented by a ball 13 meters (42 feet) in diameter; then a s
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