Continental drift plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea, and in 1928 that convection currents within the mantle might be the driving force. Holmes' views were particularly influential: in his bestselling textbook, "Principles of Physical Geology," he included a chapter on continental drift, proposing that Earth's mantle contained convection cells which dissipated radioactive heat and moved the crust at the surface. Holmes' proposal resolved the phase disequilibrium objection (the underlying fluid was kept from solidifying by radioactive heating from the core). However, scientific communication in the '30 and
Drift pin is driven in, the taper forces the two components into alignment, allowing for easy insertion of the fastener. Unlike most punches, force should never be applied to the tip of drift pin. Drift pins are especially useful for aligning fastener holes in structural steel members. Spud wrenches used for assembling trusses and steel beams have tapered handles to use as drift pins. Drift pin In metalworking, a drift pin, drift pin punch, slave pin, simply drift, or even pokey bit is the name for a tool used for enlarging holes, or aligning holes prior to bolting or riveting metal parts