264 THE POPULAR SCIENCE MONTHLY. 



of all modern discoveries, nay, those discoveries themselves. Unfortu- 

 nately, 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 ob- 

 ject contemplated, thus giving to this blank in the field of vision its 

 most probable interpretation. From the year 1809, when Malus dis- 

 covered 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 suc- 

 ceeded 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 minutiae 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 prac- 

 tical 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 nebulas 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- 



