50 and 100 Years Ago; January 1993; Scientific American Magazine; by Staff Editor; 1 Page(s)

JANUARY 1943 Formerly, if an enemy submarine lay quietly on the bottom of the sea to avoid detection, the business of 'putting the finger' on a sub became more difficult and less accurate in its results. In the present conflict, the principle of sound reflection under water, long applied to larger merchant and war ships to maintain a continuous graphical record of the ocean's floor beneath the cruising ship, is being adapted to search out silent submersibles that endeavor to 'play possum' far beneath the waves. The exact extent to which echo-sounding devices are utilized and their scientic and mechanical constituency are among those things which cannot now be told.

In a degenerate mass of gas, when the velocities of the moving electrons begin to become comparable with that of light,the law connecting pressure and density changes. Chandrasekhar has shown that,when this is taken into account, a star of small mass (less than twice the Sun's)will settle down into a permanent state with a degenerate core, as a white dwarf,and finally as a 'black dwarf', cold on the surface; but a large mass (ten times the Sun's or more) should continue to contract without limit. It is natural to suppose that something would ultimately happen to end this process, and it may well be that the contracting star blows up, ejects enough matter to leave a residue small enough to form a degenerate core, and then develops successively into a blue, a white, and a black dwarf. At the Paris Conference of 939,Chandrasekhar suggested that some catastrophic change of this sort might be responsible for a super-nova.