13 
METEOES AND METEOE SYSTEMS. 
By W. F. DENNING, F.R.A.S., F.M.S. 
N O department of scientific research has made more rapid 
progress of late than that relating to the phenomena of 
meteors. Twenty years ago our knowledge of these bodies was 
of the most crude, rudimentary character. Eew observers had 
applied themselves diligently to the task of gathering and 
discussing observations ; and though the planetary theory of 
shooting- stars offered the most reasonable explanation of their 
appearance, yet it was admitted that the subject was involved 
in considerable doubt, and presented many points of difficulty. 
The occasional apparition of brilliant detonating fireballs, the 
occurrence now and then of remarkable star- showers, the pre- 
cipitation upon the Earth’s surface of stony masses, were facts 
which could be verified from many independent sources, and 
they set men thinking to account for the strange and startling 
freaks of Nature as exhibited in these phenomena. Could such 
bodies as aerolitic stones fall from the Moon ? Could they, after 
being expelled from the lunar craters, have met with the Earth 
in her orbit and come so far within her attractive influence as 
to have been peremptorily drawn to her surface ? Could the 
smaller shooting- stars, often seen on starlight nights, be mere 
condensations of gaseous compounds in the extreme outer limits 
of the atmosphere, rendered combustible by unknown processes 
occurring at certain stages of their formation P * These, and 
* Some of the ancient philosophers appear to have formed correct ideas 
of the astronomical nature of meteors. Humboldt says that Diogenes of 
Apollonia, who probably belonged to the period intermediate between 
Anaxagoras and Democritus, expressed the opinion that ‘ together with the 
visible stars there move other invisible ones, which are therefore without 
names. These sometimes fall upon the Earth, and are extinguished, as took 
place with the star of stone which fell at vEgos Potamoi.’ Plutarch, in the 
Life of Ly sander, also says, ‘Falling stars are not emanations or rejected 
portions thrown off from the ethereal fire, which when they come into our 
atmosphere are extinguished after being kindled; they are rather celestial 
bodies which, having once had an impetus of revolution, fall, or are cast 
