J. F. Campbell Collection > Campbell's registering sun-dial

GOOD WORDS.
crossed, may be seen also. Mathematicians
may be able to explain the whole. That I
cannot do. But I have set the point of a
pencil of light to engrave, to model, aad
to make pictures of itself, and to teach me a
lesson practically. It seems now that the
jostling of light waves where they meet is the
power which works in a cone of light by
separating particles. The rays seem to do
little work when they diverge after they have
crossed the axis.
" What are you trying to find out?" said a
friend one day. " If I knew everything, I
would not try any more." I don't know what
more I may happen to find in the focus of a
burning-glass I A good many people have
found things there which they did not know
till they had tried experiments. They found
the spectrum, and lines in it, and part of
their meaning ; they found out how to make
spectacles, and telescopes, and microscopes,
and lighthouse apparatus, " dioptric and ca-
tadioptric;" they found out Daguerreotypes,
and photography, and other arts. Like other
seekers after knowledge I have been seeking
light ; and haply, by perseverance, anybody
may discover something besides danger even
in a paper \vei:;ht. Let me add one word
of warning. It is very dangerous to " play
with fire," and still more dangerous to play
with sunshine or bright lights. The writer
damaged his own eyes seventeen years ago
by looking at the electric light with a lens,
to see what was going on between the carbon
points. To look at the sun through a
burning-glass would destroy an eye in a
moment, or possibly kill a seeker after know-
ledge, devoid of caution. A hot poker thrust
into an eye would be " dangercus," and the
locus of a big lens is as hot as red iron. The
focus of a big lighthouse apparatus will now
do all the work that was detailed in Sir
David Brewster's article on " Burning instru-
ments." Part of that work was to fuse pla-
tinum, which melts at 3280°, according to a
table constructed by Dr. Alfred S. Taylor in
1845. Therefore take warning from a burnt
child who dreads fire, that good servant,
who is a bad master and a worse divinity,
Ra,
Fig. 5. — Bloc'-: enrjraved by the sun upon an equatorial slope, with a sphere 4"8 inches in diameter, June 4, 1870.
Set Q.30 A.M. ; moved 3 p.m. ; proved and sent to the Editor of Good Words at 5 p.m Niddry Lodge, Kensington,
London, W. Blue sky ; passing clouds ; fresh breeze N.W., the first fine day in the year.^. F. Caupbkll.