of all modern discoveries, nay, those discoveries themselves. Unfortunately, however, he observes, truth and error are here both equally the work of chance; the opinions here stated are like lottery-tickets, whose value is known only after the drawing.
But it is further shown by Littrow—and this is a point to which less attention had been directed—that the ancients were incapable even of observing scientifically.
That the eye must be trained, we know from physiology. The vast majority of mankind have no suspicion that we constantly see double images, but that we very properly disregard them. But few persons note the subsequent images remaining in the eye after having looked on an object, the opacity of the visual media, occurring even in the state of perfect health, or the hallucinations that precede sleep. It was only two hundred years ago discovered by Mariotte, that in each eye we have a blind spot, over which we throw the ground-color of the object contemplated, thus giving to this blank in the field of vision its most probable interpretation. From the year 1809, when Malus discovered the polarization of light, observers like Arago, Biot, Fresnel, and Brewster, had vainly endeavored with the naked eye to distinguish polarized from ordinary light. But since 1844, when Haidinger succeeded in doing this, the yellow tufts which bear his name belong, for every trained eye, to the normal aspect of the blue sky.
In the domain of tone-sensations, the harmonic notes, as we know, at first evade our immediate perception, though the timbre they give to the sound is at once noticed by every one, except those portions of the German race whose vocalization is faulty.
With such minutiæ as these, however, we are not here concerned, but with such striking objects as the stars, for the observation of which the ancients, under their favoring skies, had far better opportunity than ourselves; and which, furthermore, were to them of the greatest practical importance, both on land and sea, before the discovery of the mariner's compass. Yet the elder Pliny states the number of observed stars, i. e., of the stars according to him visible to the naked eye, as only 1,600; while Argelander reckoned 3,256; and Heis, to whom the stars appeared as points without rays, added to the last figure 2,000 more. To all this add the fact that the ancients, owing to their living in lower latitudes, could survey a larger portion of the celestial sphere than we can [in Germany]. The stars noted by the ancients decrease in number as they rise in the order of magnitudes, though, in fact, each successive class of magnitudes embraces more stars than all the preceding classes taken together. Of nebulæ and star-clusters, five were known to Ptolemy; Argelander saw nineteen with the naked eye. Hipparchus and Ptolemy take no note of the nebula in Orion, or of that in Andromeda. But the most striking circumstance of all, perhaps, is the fact that the ancients did not count the Pleiades correctly, though their number was matter of dispute, and hence an object of keener ob-
