The inhabitants of Earth learned last week that there is another planet, beside the eight they knew about, revolving around the Sun as the earth does. A few , of Earth's inhabitants had known the news for some time. The late Percival Lowell (1855-1916), rich traveler turned astronomer, elder brother of President Abbott Lawrence Lowell of Harvard University and of the late poetess Amy Lowell (1874-1925), in 1915 had predicted the existence of another member of the Planet System on its outer fringe.
The great gravities of the planets affect each other as they circle around the Sun and make their orbits slightly irregular. It was man's mathematical ability to measure such orbital variations that permitted Astronomer Lowell to declare that an unknown planet was butting Neptune's orbit out of its regularly irregular shape and to predict just where in the heavens a sufficiently powerful telescope, which did not exist during his life, would reveal it.
For many years the astronomers at the Lowell Observatory, which Percival Lowell built with his own money at clear-aired Flagstaff, Ariz., have been pointing their telescopes to the path in the skies where he had said his planet would be moving. The night of last Jan. 21, Clyde W. Tombaugh, 24, an assistant at the observatory, saw a strange blotch of light on a new plate. He hastily took the photograph to Vesto Melvin Slipher, director of the observatory. Dr. Slipher joyfully notified his younger brother, Earl Carl Slipher, and the rest of the staff, including Carl Otto Lampland. They were quite excited. Here visibly was Percival Lowell's proof. Night after night they rephotographed the planet. Pictures showed that it moved slightly in the same direction as the other planets. This was additional proof. They might have shouted out their find at once. But they deliberately saved the news until March 13. That date had a double significance in astronomy. On March 13, 1781, Frederick William Herschel (1738-1822) had, while sweeping the skies with a telescope, seen Uranus, first planet recognized in modern times.* And on March 13, 1855, Percival Lowell was born.
Astronomer Lowell's calculation of the planet's existence was gloriously praiseworthy for human mentality. But it was not unique. Neptune was discovered Sept. 23, 1846, in precisely the same manner— by figuring from the orbital variation of Uranus. Wholly independent of each other John Couch Adams, young Englishman, and Urbain Jean Joseph Leverrier, young Frenchman, did the mathematical work.
Little, of course, is yet known about the New Planet. Estimates indicate that its diameter is at least as large and perhaps two and one-half times that of the Earth, that it is 50 times farther from the Sun, that its year is 300 times that of the 'Earth's. It gets so little heat from the Sun that most substances of earth would be frozen solid or into thick jellies.