64 JOURNAL AND PROCEEDINGS. 



compression of the air. To illustrate this, I may mention that there 

 is a little instrument called an air match, consisting of a piston and 

 cylinder, somewhat like a syringe, in which a light can be struck by 

 suddenly forcing down the piston upon the air below in the cylin- 

 der. As the air cannot escape it is suddenly compressed, and gives 

 out a spark sufficient to ignite a piece of tinder at the bottom of the 

 cylinder. Some idea from this may be formed of the heat evolved 

 by the motion of a large body in the atmosphere with the velocity 

 of a meteor. A combustible body, under such circumstances, would 

 be speedily ignited^ but could not burn freely till reaching air of 

 greater density ; thus, on entering the lower portion of the atmos- 

 phere, it would burn with great rapidity, and, accordance to its 

 distance, be more or less, or entirely consumed before reaching the 

 earth. It has been estimated that by the time they have traversed 

 a space of 50 miles, the meteoroid, or meteor, as it has then become, 

 is heated, melted, evaporated and extinguished in a period of not 

 less than a second of time. The height from us at which they be- 

 come heated to visibility is sometimes as much as 200 miles, but 

 the average has been put down at 75 miles, and extinction about 50 

 miles above the earth. The length of the arc or course they de- 

 scribe in their visible path varies greatly, owing to the position of 

 the observer. One may flash up, increasing 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 

 30 or more miles apart, it would exhibit an arc 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 shattered 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 con- 

 tinue 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 

 acknowledged to exist. This resistence would change their orbits, 

 and the lighter particles would form a more erratic orbit than the 



