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intervals, which are accurately known, till they become very 
faint, if not almost invisible, and then in a period of equal 
length resume their brilliancy ; others have been known to 
blaze out suddenly, with a brightness denoting a conflagration 
on a scale which we can scarcely imagine ; and many of my 
hearers will remember the star near e Coronae which suddenly 
burst out in this manner in the year 1860, and was estimated 
as of the 2nd magnitude. The spectroscope immediately showed 
Dr. Huggins that this wonderful change in the star was due 
to a great evolution of hydrogen and other gases occasioned 
by some internal convulsion. All persons will remember a 
similar instance which occurred in the time of Tycho Brahe. 
Thus all tends to prove that the state of things which we see 
around us is not, and is not intended to be, constant and 
changeless ; and he, in my opinion, philosophizes most safely 
who looks up with adoration when he has come to the limit 
of his knowledge to the Almighty framer and preserver of 
these countless and wonderful systems. 
But discovery has gone on at an equal pace in other directions. 
Of these I can only mention some of the most important 
instances. Our knowledge of the nature and physical compo- 
sition of comets is very much increased since the year 1866, 
when the large swarm of November meteors attracted so much 
attention, and the labours of Professors Newton, Schiaparelli, 
Adams, and others, were the means of identifying the orbit 
which they described round the sun, with that of the comet 
discovered by Tempel in 1866, or Comet I of 1866. In the 
same way the orbit described by the Perseids was identified 
with the third or bright comet of 1862, which has a period of 
revolution of about 124 years. Other remarkable coincidences 
between comets and meteor-swarms have been confirmed or 
suspected, especially in that which occurred on the evening of 
November 27th, 1872, the orbit of the meteors being found to 
be the same with that of Biela’s comet. In this instance it is 
believed that the comet itself, in its passage, either touched 
or passed across the earth. Comets then apparently are 
nothing but aggregations of matter of very small density 
and consisting of very small discrete particles, which have been 
most probably thrown off from the sun, or from other more 
remote systems, and have come within the sphere of the sun's 
attraction. Between fifty and sixty (probably more at this time) 
of such systems are known to exist, though the most remark- 
able are those which I have mentioned. In this particular, then, 
we have more correct notions of the solar system than our fore- 
fathers had ; but there is nothing in our additional knowledge 
