Knoxville daily chronicle. [volume] (Knoxville, Tenn.) 1870-1882, 1873-01-09
BOOK Notices.

-#'H51 7D O. Book Notices. ;.eaie1' o.
"Ligbt and Electricity" Notes of two
courses of lectures before the Royal In
stitutiOuY of Great Britain. By John
Tyndall, LID. FRS. d. Appleton
& Co. Price, 81 so.
The recent lectures in this country of
the eminent London Professor. Tyndall,
on Light" have called the public mind
to the subject with more interest, perhaps,
than it has ever been called to any alb
stract scientific subject before. No other
man has ever held such immense crowds
with such constantly Increasing attention
on subject so purely and thoroughly SCI
entific. 1t argues well for our people, and
the epithet of simply practical can no
longer with justice be applied to US as a
nation, The essence of these lectures is
embodied in the little volume before US,
and those who have not had the oppor-
tunity of hearing the lectures could not do
better than to get the book and read them.
The ordinary laws of reflection and re-
fraction Of Hight are clearly and explicitly
set forth, and simple experiments for their
verifcation are described. The various
lenses and mirrors are considered, and the
ness and brevity that Tyndall alone is
master of. The different theories of light
receive due attention. The great Newton
held that light was simply the emission of
fine particles from luminous bodies, run
ming in straight lines until turned from
their course by some intervening body.
This is commonly, known as the ..'emis-
sive" theory, and by it most of the phen-
omena of light can be accounted for. There
were some phenomena, however, which
were not accounted for by this theory in a
mind of that great prodigy, Thomas
Young.
To account by this theory, for instance
for the colored rings seen where beam of
light falls on q soap bubble, required such
turning and twisting as was not at all
pleasing or satisfactory to his accurately
scientific mind 70 He accordingly set to
work OH the ''undulation" theory, promul-
gated some time before by Huygens, and
at last succeeded in making this theory &C
count with the greatest eXactness for all
the phenomena of light the colored rings
included. SsfaFEts ~-ff~
The undulatory theory is the one now
accepted by scientists, and according to it
light is produced by the vibrations or undu-
latiOns of an ether that pervades all space.
These vibrations reaching the expansion
of the optic nerve at the back of the eye
create an irritation there that being con-
veyed by the optic nerve to the brain are
transferred into the sensation of light. In
this respect it is analogous to sound which
is produced by the impression made on the
expansion of the auditory nerve by the
undulatiOns of the atmosphere caused by
the vibrations of sonorous bodies.
1t is strange that SO simple thing as
soap bubble should make such revolution
in scientific opinion. 1t simply shows
that, from a scientific point of view, moth
ing is so simple or common as to be insig-
nificant.
This experiment of the soap bubble also
demonstrates that very curious and inter-
under certain conditions producing dark
ness, as sound added to sound may pro-
duce silence. The theory of colors, how
they depend upon the difference in the
lengths of waves of the luminous ether,
and how we can measure these wave
lengths, are all plainly set forth. The
rainbow, the stereoscope, the action of the
various glasses and spectacles, the physiol-
ogy of vision, spectrum analysis, by which
we are able to tell with great accuracy the
constituents of the sun, stars and
teresting phenomenon known as polari-
zation, and much more, are all clearly
end concisely treated. The subject Of
electricity, to which we have only space
to allude, is dealt with in the same clear
aud explicit manner ,s~-rr
7 I'VE owe much to the Messrs. Appleton
for their effort to diffuse sound scientific
knowledge among the public. They pub
| lish the other works of Mr.. Tyndall, and
of many others eminent in scientific cir
cles. In this effort they ought to be sus-
tained. IL Z A4raAHEE