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POPULAR SCIENCE REVIEW. 
tions. The Earth, as it passed the node, would year after year 
encounter no meteors until the perihelion approach of the 
cluster, when possibly the display may have occurred in the 
day-time, 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 cir- 
cumstances which conspire to prove that such must have been 
the case, and that it preceded, by many ages, the apparition of 
the Leonids, Andromedes, and some of the other periodical 
meteor-showers. The fact that it constitutes 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 individual 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 lengthening out, until, at the present 
day, it consists of a parabolic zone of meteoric pellets, through 
which the Earth passes annually on August 10. 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 rj Persei , and their physical identity is un- 
questionable. They are merely the deflections or offshoots from 
the original system which must he greatly disturbed and con- 
torted as the Earth annually intersects it. The full effects of these 
perturbations can hardly he 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 source 
of compensation for the expenditure of its materials upon the 
Earth. But though many millions of the atoms are annually 
consumed in our atmosphere, the effect of the thinning out will 
be very gradual in making itself appreciable, for, as compared 
with the vast assemblage which constitutes the main ring, the 
proportion which encounters the Earth is small indeed. As it 
is enveloped in the stream comparatively few of the meteors 
are actually intercepted. By far the greater number pass by 
untouched. If a ball is thrown up in a thick shower of rain 
it will only encounter a few drops. This may be taken as an 
illustration. The Earth, with its diameter of 8000 miles, can 
