octor. I
wish you could be here, instead of working for 40 or 50 pounds a
year at home, out of which you can save very little. Here you might
be getting at least 100 pounds, and nothing to find yourself but
clothes. But it will not do for you to come until the Doctor goes
home. I want you to write and tell me if you have any taste for any
particular profession, and if you have been making good use of your
spare time, in reading useful works. You should remember never to
waste a minute; always be doing something. Try and find out what
things you have most taste for, as they are what you should study
most; but get a general knowledge of all the sciences. Whatever
else you learn, don't forget mathematics and the sciences more
immediately deduced from them, (at the head of which stands
astronomy,) if you have any love of truth--and if you have not, you
have none of your mother's blood in you. Mathematics are the
foundation of all truth as regards practical science in this world;
they are the only things that can be demonstrably proved; no one
can dispute them. In geology, chemistry, and even in astronomy,
there is more or less of mere matter of opinion. For instance, in
astronomy we do not know for certain what the sun or stars are made
of, or what the spots are on the sun, and a few details of that
kind; but the main mathematical principles cannot be disputed. The
distance and size of the sun or of any of the planets can be
proved; the length of their days and years, and even the weight of
the matter of which they are composed. Such things will probably
appear to you impossible, if you have read nothing of them;
especially when you hear that the sun is ninety-five millions of
miles off, and that the planet Neptune, which is the farthest known
planet from the sun, is at such a distance that the light of the
sun takes about five hours to reach it; that is, the sun is
actually five hours above the horizon before the people there see
it rise. Its distance is 2850 millions of miles, and the sun as
seen by them is not larger than Venus appears to us when an evening
star. And although this planet is so distant that it can only be
seen with large telescopes, they can not only compute its distance
and size, but also the mass of matter of which it is composed. But
you will find all this thrown into the shade by the way in which it
was discovered. As I may be telling you what you know already, I
will merely state, that from observed