29 
THE TAILS OF COMETS. 
(Illustrated by the Lantern). 
By Rev. A. L. CORTIE, S.J., F.R.A.S 
February 5 th, 1907. 
Father Cortie, who spoke for over an hour, and showed 
a large number of slides illustrating the different types of 
comets and their orbits, said that etymologically the word 
comet meant “ hairy star.” As a rule comets did not belong 
to our system unless they were captured by one of the planets 
of our system. They were visitors to our system and did not 
travel round the sun in the way stars and planets did, their 
motion, as a rule, being retrograde — opposite to the direction 
of the planets and the sun. His object was to explain the 
wonderful appendage of the comet known as the comet’s tail. 
Photography has come to the aid of the astronomer, and was 
able to record the appearance and progress of the comet. He 
began with the comet of 1892, discovered by Swift, and 
photographed at the Lick Observatory by Barnard. He 
(Barnard) also photographed the comet of 1893, which illus- 
trated the multiple tails which spring from the heads of 
comets at all sorts of angles. Tails of comets were generally 
from 10 to 15 million miles long. There were tails from 30 
to 50 million miles long and sometimes they were as long 
as 100 million miles, while the head was from 10,000 
to 40,000 miles in diameter. The head of the comet of 
1843 travelled at the rate of 380 miles a second. Astron- 
omers had come to the conclusion that the tail of the 
comet was not a permanent appendage but something 
formed and dissipated and formed again. The comet of 
1901, taken at the Cape Observatory, showed a very 
tenuous substance. No perturbation was exercised on the 
planets by the comets, but a great perturbation was exercised 
on the comets themselves. The comets did not attract or 
darken the planets ; though their volume was so vast, their 
mass was something inconsiderable — perhaps something like 
one or two hundred tons. Some astronomer had declared 
that we might pack all the streams into a top-hat. That was 
doubtless an exaggeration, but the mass was certainly small 
compared with the planetary mass. The tail of the comet 
showed a hollow cone in the shape of a black rift. Another 
picture of the same comet (1901) taken in South Australia, 
showed a difference between the intrinsic brilliance of the 
