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be more or less entirely consumed before reaching the earth. It has been esti- 
mated that by the time they have traversed a space of fifty miles, the 
meteoroid, or meteor as it has then become, is heated, melted, evaporated, and 
extinguished in a period of not Jess than a second of time. The height from us 
at which they become heated to visibility is sometimes as much as 200 miles, but 
the average has been put down at seventy-five miles, and extinction about tifty 
miles above the earth. 
The length of the are or course they describe in their visible path varies 
greatly, owing to the position of the observer. One may flash up, increase in 
size and brilliancy and disappear without seemingly describing any arc. The 
course of such a one is directly towards the observer, but to another person 
thirty or more miles distant it would exhibit an are of several degrees in length. 
Different and varied views are held by philosophers as to the origin of 
meteoroids. One theory is that they are fragments of an exploded or shat- 
tered planet filling interplanetary space, most of which through holding orbits 
round the sun will ultimately fall into that body and serve as fuel for that 
central orb. To illustrate this, supposing our earth through some gigantic 
convulsion became disintegrated and burst into numerous portions, these would 
continue to move on becoming more or less erratic in their movements; the 
smaller portions would first feel the influence of disturbing agencies larger than 
the earth, and moving inward would become entangled as it were in the resisting 
medium in space which is now acknowleged to exist. This resistance would 
ehange their orbits, and the lighter particles would form a more erratic orbit than 
the heavier or denser ones. They would gravitate towards Venus, which lies 
inside our orbit, and be the first to fall on it, whilst the denser fragments 
metalloids, and metals would be the last. 
Dr. Brewster favors the theory of Meteoroids being fragments of a large 
planet similarly as the asteroids, the previous existence of which was long ago 
suggested by the vast chasm between Mars and Jupiter, where only asteroids 
have as yet been observed Dr. Olbers, the discoverer of three of the known 
asteroids, held the same idea, and that the lesser fragments coming within the 
attractive power of a planet wovld fall towards it, and when entering its atmos- 
phere would go through all the conditions referred to, fusion, luminosity, ete. 
Sir John Herschell, however, differs from this theory. The diameter of Jupiter, 
the largest known body in our planetary system, is 80,000 miles, whilst that of 
Clio, one of the smallest, is only sixteen miles. Chladin, a philosopher at the 
end of the last century, thought that bodies might exist as much smaller in 
comparison as Clio to Jupiter, having only sixteen feet diameter, and in the 
same ratio we come down to one-twenty-fifth of an inch, mere cosmic dust. 
Myriads of these may revolve in space without our having any knuwledge of 
their existence. 
To this comet dust is now attributed by scientists that peculiar fleecy’ 
brightness’ known as the zodiacal light. Any observer of the western sky at this 
season of the year for about one hour after sunset may see a soft faint cone 
shaped glow of light extending about forty degrees, following nearly the Sun’s 
path in the heavens. Near the equator when the ecliptic rises high above the 
horizon it can be seen nearly all the year round, and in a very clear atmosphere 
in the tropics has been traced all the way across the heavens from east to west 
forming a complete ring. The theory that now prevails is that the light from the 
sun when below our horizon reflects on the cosmical atoms of floating star dust 
and meteoroids is the cause of the soft celestial glow that now lingers evening after 
evening in our western sky. An illustration of this is afforded by a ray of light 
which finds its way into a darkened room through a small orifice, revealing as 
