This being a wet night, and I
having exhausted
my travelling
props, set to to write to you about what I can recollect of
my
past
history. It is curious that though the remembrance of ploys remains
longer
than that of home doings, it is not so easily imagined after
a
short
interval. By
imagining is here meant bringing up
an accurate
image of thoughts,
words, and works, and not a mere geographical summary of
voyages
and travels.
But
to the point. Perhaps you remember
going with my
Uncle John Cay
(7th Class), to visit Mr. Nicol in
Inverleith
Terrace.
There we saw polarised light in abundance. I purposed going this
session
but was prevented. Well, sir, I received
from the
aforesaid
Mr. Cay a "Nicol's prism," which Nicol had made and sent him. It is
made
of calc-spar, so arranged as to
separate the
ordinary
from the extraordinary ray. So I adapted it to a camera
lucida,
and made charts of the strains in unannealed glass.
I have set up the machine for showing
the rings in
crystals, which I
planned during your visit last year. It answers
very well.
I also made some experiments on compressed jellies in illustration of
my
props on that subject The principal one was
this:—The jelly
is poured while hot into the annular space contained between
a
paper
cylinder and a cork: then, when cold, the cork is twisted round, and
the
jelly exposed to polarised light, when a transverse
cross,
x, not +, appears with rings as the inverse square of the radius, all
which
is fully verified. Hip!
etc. Q.E.D.
But
to make an abrupt transcision,
Forbes says, we set
off to Glasgow
on Monday 2d; to Inverary on 3d; to Oban by Loch
Awe on
4th;
round Mull, by Staffa and Iona, on (5th), and here on 6th. To-morrow we
intend to get to Inverness and rest
there. On Monday
perhaps? to the land of Beulah, and afterwards back by
Caledon.
Canal to Crinan Canal, and so to Arran, thence to Ardrossan, and then
home.
It is possible that you may get a more full account of all
these
things (if agreeable), when I fall in with a pen that will spell; my
present
instrument
partakes of the nature of skates, and I can hardly steer it.
There is a beautiful base here
for
measuring the
height, etc., of Ben
Nevis. It is a straight and level road through a
moss for
about
a mile that leads from the inn right to the summit.
It is proposed to carry up stones
and
erect a cairn 3
feet high, and
thus render it the highest mountain in Scotland.
During the session Prof. Forbes
gave
as an exercise to
describe a cycloid
from top of Ben Nevis to Fort William, and slide trees down
it.
We
took an observation of the slide, but found nothing to slide but snow.
I think a body deprived of
friction
would go to Fort
William in a cycloid
in 49·6 seconds, and in 81 on an
inclined plane. I
believe
I should have written the greater part of this letter to Allan Stewart,
but I know not where he is, so you get it, and may
read it
or no as you like.
We
will be at home between the 15th
and 22d of this
month, so you may
write then, detailing your plans and specifying
whether you
intend to come north at all between this and November, for we would be
glad if either you or Bob would disturb our
solitude.
