The growing evidence for interstellar material led Pickering (1912) to comment that "While the interstellar absorbing medium may be simply the ether, yet the character of its selective absorption, as indicated by Kapteyn, is characteristic of a gas, and free gaseous molecules are certainly there, since they are probably constantly being expelled by the Sun and stars."
As crecentes evidencias sobre o material interestelar levaron a Pickering (1912) a comentar que "Mentres que o medio de absorción interestelar pode ser simplemente o éter, porén o carácter da súa absorción selectiva, como indicou Kapteyn, é característica dun gas, e alí hai, certamente, moléculas gasosas libres, xa que probablemente están sendo expulsadas constantemente do Sol e as estrelas."