30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 66 



III 



For the entire orbit from 153 km. to 57 km., as an average velocity 

 even in this case, we obtain only 4 km. or 1/18 part of the entrance 

 velocity. As before stated, the orbits of the Leonids are supposed 

 to lie between 155 and 98 km. because the particles are entirely dissi- 

 pated by the very considerable rise in temperature before they can 

 descend any lower. In fact the bodies of this stream, amon^ all the 

 shooting-stars, leave behind them the most enduring tails. It, there- 

 fore, appears proper to consider the above given plan as only 

 applicable within similar limits or between 153 and 97 km. Thus we 

 obtain on the average only about 27 km. or f of the original velocity 

 whereas from the observations the difference relative to the theo- 

 retical average is much smaller. 



Direct observations, no matter how fragmentary the data, make it 

 in general probable that the diminution of the velocity in the upper 

 atmospheric mediums is slighter, but in the latter or lower part of 

 the orbit or its lowest part which reaches far down must be greater 

 than they would seem to be according to the previous theoretical 

 views. Many optical phenomena that seem to be connected with the 

 checking of the fire balls also seem to agree with this view. 



The dependence of the altitude of the terminal point of the path 

 upon the velocity at entrance demands also some explanation. Under 

 probable assumptions (C/. Schiaparelli, p. 231 ffg.) it is proven that 

 the large but very different velocities of two bodies which enter under 

 otherwise equal conditions into the atmosphere and pass through it 

 in straight line orbits are diminished by the resistance in such a way 

 that at any given altitude they attain almost the identical velocity. 

 In the examples I and II this velocity is attained at the altitude 62 km. 



We must not however conclude from this that the terminal altitude 

 is independent of the entrance altitude. For the meteor occurring at 

 the greatest altitude should convert much more kinetic energy into 

 heat and would therefore be much more rapidly consumed. 



