Rocky Mountain husbandman. [volume] (Diamond City, Mont.) 1875-1943, 1877-11-01
NJ ISC III A n &c U.s..
THE VELOCITY OF LIGHT.

VA VI li@1AG Il y hlioN - liz LAIN PAiotpei hIii
&c world, has been followed up in his re-
searches, it seems, III. A. Cornu, so far as
the determination Of its velocity is coacern-
cd. M. Fizeau has made the subject of
light quito his own, and in the carly days Of
daguerreotype, he did much toward i'm
proving and celebrating the process. Iie it
was who first of all distinctly comprehend
ed the fact that so long As only one image
could be secured BY the daguerrcotype pro-
cess, the application Of the latter must be
very limited. 1t was his endeavor, after an
Image had been once secured, to produce
therefrom other duplicate images-a prob
tenn which Fox Talbot had already solved
duction of negatives instead Of positives.
Fizeau's daguerreotype engraving process,
by which he sought to convert the daguer-
reotype plate into a printing block, from
which Impressions might be printed in the
press, although a singularly ingenious one,
turnetl out of little practical value since 1t
was impossible to produce half tones by its
means in any degree Of perfection ; and the
strides made at the same time by the appli-
cation of collodion and glass plates to pho
Biography at once placed NJ. Fizeau for be-
hind, and he abandoned a line Of research
which, at one time, babe fair to ensure him
considerable reward. But he did not for
sake the shrine, at which he had so long
worshipped ; he simply devoted himself to
some other portion Of the vastsubject which
he had made his own. This was to ascer-
tain the velocity with which light travels, a
matter which, as everyone who has studied
light knows, is beset withpeculiar difficulty.
According to n. Fizeau's experiments, the
velocity of light was ls5, 157 miles per sec
ond; and when we mention that, after some
very elaborate researches undertaken by NJ.
Cornu, this gentleman finds thatthe veloci-
ty is represented more accurately by 1885,
80 miles per second, we can only wonder
at the accuracy with which NJ. Fizeau con-
Quoted his investigation. Unfortunately, in
Il delicate research like this. it is impossible
10 exclude errors of all. kinds, and we must
take, therefore, both the results of M. Fig
eau and N. Cornu as approximate truths on
ly; still they are both SO near one another
that we may, at any rate, conclude that
light travels in any case at the extraordina-
ry velocity Of more than $4,000 miles per
second. We have no such trustworthy da-
ta in respect to the velocity with which cleo,
tricity travels, for in this case the estimates
made by various philosophers differ widely
from one another. Thu FizeauA estimates
the velocity of the electric spark. through
:Ya,, at 80 100 milns Nor. cecanI5s and tIarnIYuh
copper at Ill ,7S0, miles while Wlleatstone's
results seemed. to, prove that the velocity
was as mucln as, 2sS, 600 miles per second.
kirchpfsa.. the. German philosopher, tells us
that the motion of electricity i'll a wire where
it meets with no resistance should be 1922
a24, which is. the same as light IN racuo.
Photographers may be interested to know
how it is possible to determine the rate Of
travelingyof SO rapid a medinm as light, and
we therefore try TO explain the method
adopted by NJ. Cornu in as few words as
possible. There is a toothed wheel which
r~evolves at a rapid and known velocity. A
powerful ray of light, which may be term
cd pin-pointcd, is allowed to- pass, through
one Of the inches in the wheel, and: as. the
wheel revolves. the point Of light is obscured
.wheneNera tooth passes. We will imagine
the wheel at rest for a moment, and this
ray Of light shining through one Of the
inches. BY having recourse to ,suitable len
ses and a rejecting surface upwards at the
proper angle, this ray of light is sent, on a
journey OF 10000 meters--in fact, from the
Paris Observatory fO the Fort Nalarian be-