i8o THJiJ POPULAR SCIENCE MONTHLY. 



of brilliant displays at the end of July. Then there occurred a break 

 until eighty-three years later, when it several times reappeared with 

 fiimilar splendor. A wide interval of more than three hundred years 

 brings us to the year 1243, when it seems to have been again recog- 

 nized, after which, until 1709, there is only one other observation of 

 the shower (in 1451). During the last hundred years it has, however, 

 been frequently observed, though many of the recent displays can not 

 be compared with those of ancient times. The intermittent and rare 

 character of the shower, as it existed between the tenth and eighteenth 

 centuries, proves that few returns were of a sufficiently imposing na- 

 ture to be recorded, and that possibly the conditions were opposed to 

 its appearance. If the meteors of the orbit during that period were 

 condensed in the region of their derivative comet, then we can under- 

 stand the singular paucity of observations. The earth, as it passed 

 the node, would year after year encounter no meteors until the peri- 

 helion approach of the cluster, when possibly the display may have 

 occurred in the daytime, and been of such brief duration as entirely 

 to elude detection. 



The entry of this stream into the solar system probably dates back 

 to a very remote antiquity for there are several circumstances which 

 conspire to prove that such must have been the case, and that it pre- 

 ceded, by many ages, the apparition of the Leonids, Andromedes, and 

 some of the other periodical meteor-showers. The fact that it consti- 

 tutes an unbroken ring leads to the inference that it must have existed 

 from the earliest times in order to bring about so complete a dispersion 

 of its particles, for on its first introduction, as a comet, to the earth, it 

 is to be assumed that it formed a condensed mass like the Leonids, 

 and only appeared as a meteor-shower when the comet returned to 

 perihelion. A very slight difference in the periodic times of the indi- 

 vidual meteors following the nucleus must have eventually distributed 

 them (by its cumulative effects) along the entire orbit. In other 

 words, the original group must have undergone a process of lengthen- 

 ing out, until, at the present day, it consists of a parabolic zone of 

 meteoric pellets, through which the earth passes annually on August 

 10th. Moreover, the radiant point of the shower often fails to become 

 sharply defined. Several concentric streams of similar meteors appear 

 to diverge from the region about r] Persei, and their physical identity 

 is unquestionable. They are merely the deflections or offshoots from 

 the original system which must be greatly disturbed and contorted as 

 the earth annually intersects it. The full effects of these perturba- 

 tions can hardly be estimated : many of the particles must be diverted 

 into new orbits, and one of the results upon the main stream may be 

 a constant widening out, so that the apparent duration of the shower 

 must go on increasing. It now actively extends over at least eight 

 nights ; hence the width must exceed 10,000,000 miles. And some 

 diminution in its intensity must occur at each return, unless there is a 



