The 48 constellations (21 northern, 12 zodiacal, and 15 austral) indicated by Ptolemæus, contain a total of 1026 stars, whose relative positions had been determined by Hipparchus. To undertake an enumeration of the stars, and to transmit the result to posterity, appeared to Pliny an audacity before which even a god would have recoiled (_Hipparchus--ausus, rem etiam Deo improbam, annumerare posteris stellas_).[11]
Yet numerous doubts had already risen in the mind of Hipparchus as to the accuracy of the number recognised. In the first place, the ancients undoubtedly knew, as we do, that the visual faculty is not the same in all individuals; that there are some who, in the same celestial space, see more stars than others. Many persons can discern up to stars of the seventh magnitude, while with others the sight fails far within that limit. The ancients must also have known, as we do, that, for the enumeration to be complete, the sky must be observed from all the points of the terrestrial surface on which man is planted. Even in our own days the catalogues of the southern heavens are far from being perfect. Finally, more than two thousand years before the time of Galileo, Democritus had already enunciated the opinion that the Milky Way was a mass of innumerable stars. All these signs should have been accepted as warnings against premature affirmations.
The invention of telescopes suddenly enlarged the question, and it became necessary to establish a line of demarcation between the number of stars visible to the naked eye and the number visible through the agency of the telescope. Argelander, the author of the "Uranometria," has found that the stars visible to the naked eye, over the entire surface of the heavens, range from 5000 to 5800. Otto Struve, employing Herschel's method of computation, has estimated at upwards of twenty millions (20,374,034) the number of stars visible with the Herschel 20-feet telescope.
But, in presence of all the nebulæ resolvable into stellar masses, and before the development of the artificial range of our sight,--in presence, finally, of that hopeless perspective which the more we discover the more we perceive how much there remains to discover,--are we not forcibly carried back to our point of departure?