PROGRESS DURING THE NINETEENTH CENTURY. 
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of an imaginary planet that might cause these irregularities ; their 
results, which were practically identical, were communicated to 
Dr. Galle at Berlin on September 23rd, and the same evening he 
discovered Neptune in the spot indicated. 
In the first half of the century it was discovered that the periods 
of comets got altered by their passing near planets; in the next 
quarter that shooting stars are portions separated from a comet, 
which come into the earth’s atmosphere. And during the last 
quarter, and especially during the last few years, much has been 
discovered by means of the spectroscope, not only as regards the 
chemical elements to be found in the stars, but also as regards 
their motion through space. At the Lick Observatory, with its 
excellent instruments and favourable atmosphere, it has been proved 
by the spectroscope that about one star in each dozen is a binary 
system, that is to say, it has at least one planet revolving round 
it, a planet which is in itself absolutely invisible to us by any 
known instrument. Yet the marvellous accuracy and sensitiveness 
of modern scientific instruments is such that astronomers seem able 
to investigate anything that enters their mind. Lor instance, 
a Chicago astronomer has calculated that the heat given out by 
the star Yega is equal to that radiated by a candle at a distance 
of 8 miles. Possibly we may feel that this discovery, like that 
of the Nova Persei, and indeed of all other astronomical discoveries, 
is of very little practical value ; and some may even doubt whether 
we shall learn much by any message from Mars—when we get it— 
and I will therefore say no more on this subject, but pass at once 
to the last branch of knowledge to which I shall refer, and one 
to which we are all more or less indebted for help in the past. 
I mean the science of Medicine. 
Undoubtedly more progress has been made in medicine during 
the past century than had been made in the previous two thousand 
years, thanks not only to the improvements made in microscopes 
and other scientific instruments, but also to the greatly-increased 
knowledge of physics and chemistry, and especially to the adoption 
of scientific methods of investigation. The following are some of 
the more important advances of medicine. 
Yaccination was introduced instead of inoculation for smallpox 
between 1790 and 1801. The stethoscope was introduced about 
1815-25. Of ansesthetics, nitrous oxide, the properties of which 
were discovered by Sir H. Davy in 1800, was first used by dentists 
in America in 1844, and Dr. Morton in the same country began using 
sulphuric ether in 1846, in which year it was also used in England, 
chloroform following in 1847. Cocaine is a much more recent 
