John Henry Reynolds was a British astronomer who served as the president of the Royal Astronomical Society who frequently corresponded with American astronomer Edwin Hubble, developed a formula for measuring the surface brightness of what? 
John Reynolds (astronomer): John Henry Reynolds (1874–1949) was a British astronomer who served as the president of the Royal Astronomical Society between 1935 and 1937 and is known for his work on the classification of stellar bodies. John Reynolds (astronomer):  The Hubble–Reynolds law, a formula for measuring the surface brightness of elliptical galaxies, is named after them. Edwin Hubble: Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer.
elliptical galaxies