At the Spring 1974 meeting of the American Physical Society in Chicago, Jeremiah P. Ostriker, an astrophysicist from Princeton, read a paper¹ which made news all over the United States. In view of the particular problem which gave rise to the paper, the excitement should have seemed out of proportion. It was an old story that rotating gravitational systems like our system of planets and the system of stars composing our galaxy or other spiral galaxies obey Kepler's laws, the third of which states a very specific ratio for the decrease of orbital speed with distance from the center. It is an equally old story that Kepler's laws can be derived from Newton's investigations of the mutual attraction of moving masses according to the inverse square law. If it had been known around the turn of the century that the observed orbital velocities of stars in our galaxy did not fit the ratio in question and if it had been proposed that more mass ought therefore to exist in the galaxy, no particular excitement would have ensued. Around the turn of the century, the Universe was pictured as containing an infinite amount of mass and the value of the average density of matter could not be considered critical.