of enlightenment in cosmology had begun. Both Shapley and curtis were present.

The way was now open for a new attack on the cosmological problem which had hitherto been the concern of theoretical investigators. Two lines of research were possible for the observer to pursue, and Hubble was a pioneer in both. On the one hand, he studied the contents and general structure of galoxies. On the other, he investigated their distribution in space and their motion. Both approaches were strongly motivated by his belief that galaxies are the structural units of matter that together constitute the astronomical universe as a whole.

Hubble was the first to introduce a significant classification system for galaxies. He presented this at the meeting of the International Astronomical Union at Cambridge, England, in 1925of his life, radio and optical evidence was forth-coming that the same situation prevails in our own galaxy.

In 1942 war again caused Hubble to divert his energies from astronomy. He had long been aware of the dangers that threatened the free world and was chairman of the Southern California Joint Fight for Freedom Committee. After the United States entered the war, he sought active service in the army but was asked instead by the U.S. War Department to become chief of ballistics and director of the Supersonic Wind Tunnel Laboratory at the Aberdeen Proving Ground, Maryland. He remained there until 1946 and was awarded the Medal of Merit for his services.

After the war Hubble devoted much time to plans relating to the Hale 200-inch telescope. He became chairman