depend upon the elastic constants of the materials through which they pass, in particular the bulk modulus and stiffness. It should be possible to combine the experimentally-determined wave velocities of the various parts of the Earth's interior and the elasticity data from various rocks in order to find out about the Earth's interior. However, by the early 20th century no one had been able to determine the elastic constants of common rocks, because almost all rocks are slightly porous, complicating conventional elasticity measurement methods. Adams was able to solve this problem by fashioning rocks into cylinders, putting thin hermetically sealed metal jackets around them, and subjecting them to high pressures while inside a mobile liquid in a pressure vessel. By recording the piston displacement required in order to achieve a given pressure, Adams could find the volume change of the rocks and their bulk modulus. Implications These experiments had important implications for the field of geophysics. Adams used the measured bulk modulus of various rocks to find their wave velocities and then compared his results with the wave velocities of the Earth, which had been determined through seismology. He concluded that the high central density required for the known density of the Earth could not be accounted for by the compression of ordinary silicate minerals; the inner core of the Earth must be composed of a heavy iron-nickel material. In addition, research performed by the Croatian seismologist Andrija Mohorovičić indicated that there exists a region of the Earth's interior, the Mohorovičić discontinuity, where high wave velocities coincide with shallow depths. Adams' work showed that only two minerals, dunite and eclogite, could possible make up the discontinuity, and further exploration showed that dunite was a better fit than eclogite. Therefore, by combining his own elasticity calculations with current seismographic research, Adams was able to show that the conventional view of the Earth's interior as a uniform molten liquid was false, and that the Earth is in fact composed of a nickel-iron core, a thin crust, and that aside from a thin layer of dunitic material between the Earth's crust and mantle, the rest of the Earth's interior is iron, magnesium, silicon, and oxygen. Awards and honors 1910: Elected to member of the Philosophical Society of Washington (and president in 1929) 1921 or 1924: Edward Longstreth Medal of the Franklin Institute 1943: Elected to member of the U.S. National Academy of Sciences