Evidence in favour of the spiral hypothesis of the Milky Way, as advocated by Easton and Scheiner, may be found in Kapteyn's researches on the proper motions of the stars. This eminent astronomer finds that stars with measurable proper motions--and therefore in all probability relatively near the earth--have mostly spectra of the solar type, and seem to cluster round "a point adjacent to the sun, in total disregard to the position of the Milky Way," and that stars with little or no proper motion collect round the galactic plain. He is also of opinion that the Milky Way resembles the Andromeda nebula, "the globular nucleus representing the solar cluster, and the far spreading wings or whorls the compressed layer of stars enclosed by the rings of the remote Galaxy." With reference to the plurality of inhabited worlds, it has been well said by the ancient writer Metrodorus (third century B.C.), "The idea that there is but a single world in all infinitude would be as absurd as to suppose that a vast field had been formed to produce a single blade of wheat."[474] With this opinion the present writer fully concurs. CHAPTER XXI General The achievements of Hipparchus in astronomy were very remarkable, considering the age in which he lived. He found the amount of the apparent motion of the stars due to the precession of the equinoxes (of which he was the discoverer) to be 59" per annum. The correct amount is about 50". He measured the length of the year to within 9 minutes of its true value. He found the inclination of the ecliptic to the plane of the equator to be 23° 51'. It was then 23° 46'--as we now know by modern calculations--so that Hipparchus' estimation was a wonderfully close approximation to the truth. He computed the moon's parallax to be 57', which is about its correct value. He found the eccentricity of the sun's apparent orbit round the earth to be one twenty-fourth, the real value being then about one-thirteenth. He determined other motions connected with the earth and moon; and formed a catalogue of 1080 stars. All this work has earned for him the well-merited title of "The Father of Astronomy."[475] The following is a translation of a Greek passage ascribed to Ptolemy: "I know that I am mortal and the creature of a day, but when I search out the many rolling circles of the stars, my feet touch the earth no longer, but with Zeus himself I take my fill of ambrosia, the food of the gods."[476] This was inscribed (in Greek) on a silver loving cup presented to the late Professor C. A. Young, the famous American astronomer.[477]