Page:Popular Science Monthly Volume 9.djvu/465

Rh good eyesight. In a didactic poem by Aratus, written 270 years, we have our earliest trustworthy account of Grecian astronomy. There the Pleiades are called "έπταπόροι"—stars traveling in seven paths—though according to Aratus only six stars were visible. Some 300 years later Ovid writes—

while Hipparchus, in his critique of Aratus, about 150 years before Ovid, expressly says that in clear, moonless nights seven stars can be actually made out. Now, Aratus lived in Macedonia, and Ovid apparently wrote his "Fasti" at Rome, giving the finishing touches to the work on the southern shore of the Black Sea: thus both writers lived beneath a very clear sky. The fact that Hipparchus labored at Rhodes, a few degrees farther south, must not be supposed to account for his having seen one more star than the others, though the discrepancy between the observers is all the more surprising as the group about which they differed was of great importance for navigators in the then state of nautical science, and was constantly under observation. This circumstance, in fact, attracted the attention of the astronomers of the time, but for centuries they sought in vain for the seventh star, and offered all manner of curious explanations for its supposed disappearance, one of which is worthy of special mention, viz.: that this seventh star had moved over to the position of the middle star in the tail of Ursa Major, called by the Arabians Mizar, and that it was the little star now commonly known as the Postilion and which stands close to Mizar. The scholia to Homer cling to this idea of the disappearance of the seventh star. Not until the thirteenth century do we find a correct description of the Pleiades, in a work by the Persian astronomer Kazvini, who apparently borrowed it from Sûfi. "There are," says Kazvini, "six stars (in the Pleiades) and in the midst of them a number of dark (i. e., faint) stars;" but his observations received no attention from subsequent astronomers. In vain, too, was the observation even of such a man as Maestlin, Kepler's preceptor, who distinguished no less than fourteen stars in the Pleiades group. Not till after the invention of the telescope could Sir Christopher Heyden, in 1610, write as follows, showing the power of the new instrument: "I see with my telescope eleven stars in the Pleiades, though never before were more than seven distinguished." But how stands the case to-day? At present they who discern these eleven stars with the naked eye are considered anything but prodigies; indeed, I am acquainted with persons—not professional astronomers, but laymen—who can make out from fourteen to sixteen stars in this group. But then we are the descendants of generations of men who from infancy were taught to put their organs of sense to the sternest test, and to take note even of the faintest sense-impressions; our eyes have been schooled, and