The Republican., 1889-04-06
POPULAR SCIENCE,
Researches Into the Velocity of Light,
Electricity and Sound.

Researches Into the Velocity of Light,
Electricity and Sound.
From an observation of the eclipses
of Jupiter's first satellite. in 1915, Ro-
mer, Danish astronomer, deducted
the velocity of light, his calculations
establishing for it velocity of 100000
miles per second.
M. Foucault succeeded in determin-
ing the velocity of light experimentally
by means of an apparatus based upon
the use of the rotating mirror, and
calculated it to be 185, 157 miles per
second.
In 1S49 M. Fizeau measured the ve-
locity of light directly, by ascertaining
the time it took to travel from Suresnes
to Montmartre Ga distance of %. 334
feeO and back again. making a total
travel of five and three-quarter miles,
nearly. He made use of a toothed
wheel revolving at certain known vc-
locities; pencil of rays being trans
mitted through an interval between
two teeth of the wheel, which was
placed at Suresnes, was reflected by
mirror placed at Montmartre, through
series of tubes and lenses, directly
back to the wheel. He found the
velocity of light to be 1856, 900 miles per
.-sccnd.
The mean of the three values above
given is 190,3S5 miles, and the value
generally taken as the velocity of light
very nearly agrees with it, being 19O,-
600 miles per second.
Wheatstonc, by the employment of a
rotating mirror and an interrupted coil
to give sparks, ascertained the velocity
of electricity to be $3.50 miles per
second.
Kirchotf estimated this velocity in a
wire where it met with no resistance to
be 1924 miles per second. But ac-
cording to NM. Fizeau and Gounelle,
its velocity with an iron wire is 62, 100
miles, and with a copper wire 111,7S0
miles per second. These measure
ments, however, were made with tele-
graph wires. which induce opposite
electricities in the surrounding media,
thus producing q resistance which re-
duces the velocity. The nature OF the
conductor has some influence on the
velocity; but not the thickness of the
wire, nor the tension of the electricity.
Direct measurements to ascertain the
velocity of sound were made by Moll
and Van Beck in 1928. Two hills near
Amsterdam, 57,971 feet apart, were
taken as stations, and cannon were fired
at stated intervals simultaneously at
both stations, and the elapsed time be-
tween seeing the flash and hearing the
sound was noted by chronometers.
From these experiments the velocity of
sound was estimated to be 1,092.7S feet
per second in dry air. But it has been
found that the velocity varies with the
temperature-i. e., at 32o Fahr, the
velocity of sound is |. .0J0 feet per second
and that for every degree of tempera-
ture above this l feet must be added
to the velocity. Fogs or rains unac-
companied by winds, do not interfere
with the velocity of sound, but
wind alone will interfere with
its velocity materially. There is some
reason to believe that loud sounds
travel somewhat faster than low ones,
which was first remarked by Prof.
Mullet while carrying on blasting near
Holyhead
In water the velocity is about 4,70S
feet per second, nearly four times as
much as in air; in wood, from $4,000 to
10000 feet; in iron, 1900 feet; and in
copper, 10, 500 feet per second. Safety
Valve.