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Philippine Journal of Science 
planetary space into the outer air. Various observers have 
deduced for the height at which they appear values ranging from 
112 kilometers, for the slow Perseids of August, to 155 kilo- 
meters, for the swift Leonids of November; 180 kilometers is 
given as the average result of work at the Berlin Observatory, 
and even 200 kilometers by an English observer. These heights 
may be compared with the heights of 149.3 kilometers (average) 
and 181.6 kilometers (best) found above. 
Neither the optical nor the meteor results give the extent of 
the atmosphere. The observations on dawn show that above the 
computed height there are enough molecules to scatter light in 
total sufficient to influence the eye; the meteors go a long way 
through the vacuumlike outer atmosphere before they become 
incandescent. But it would seem that the amount of the outer 
air which is competent to produce the one effect is also com- 
petent to produce the other. 
For the loan of books and for friendly criticism of this paper 
thanks are due to Father J. Cornelias, of the astronomical de'- 
partment of the Manila Observatory. 
