The Sun.
London, England, 1851-05-08 00:00:00

INSTITUTION OF CIVIL ENGINEERS.
On Tuesday, April 29, (Wm. Cubitt, Esq., President,
n the chair), previous to the ordinary meeting, Mr.
Joseph Whitworth (Manchester) exhibited, in the
Library, a new measuring machine, for determining
minate differences of length. The accuracy of the ma-
chine was demonstrated by placing in it a standard yard
measure, made of a bar of steel, about three quarters of
an inch Square, having both the ends rendered perfectly
true. One end of the bar was then placed in contact
Ice. with the face of the machine, and at the other end, be-
- t meen it and the other face of the machine, was inter-
posed a small flat piece of steel, termed by the experi-
menter " the contact piece," whose sides were also ren-
dered perfectly true and parallel. Each division on the
micrometer represented the one millioneth part of an
inch, and each time the micrometer was moved only one
division forward, the experimenter raised the contact
piece, allowing it to descend across the end of the bar
uy its own gravity only. This was repeated until the
closer approximation of the surfaces prevented the con-
tact piece from descending, when the measure was com-
pleted, and the number on the micrometer represented
he dead length of the standard bar to the one millionth

part of an inch.
Eight repetitions of the experiment in a quarter of an
hour produced identical results, there not being in any
, cafe.a variation of one millionth of an inch.
This method of operating was termed "the system of
proof by the contact of perfectly true surfaces and gra-
vity;" and in connexion with it was shown another in-
teresting experiment.
When the micrometer was up within one division of
the number where contact would be presumed to occur,
the application of the finger to the centre of the steel
bar sufficed to expand and lengthen it instantaneously,
so as to prevent the descent of the "contact piece."
The other method of proof was by having a small
simple battery composed of a piece of zinc soldered on
to a piece of copper aed plunged into rain water, with-
out the admixture of any acid; this was connected with
the two ends of the measuring machine, and also with a
delicate galvanometer. On pursuing the same process of
advancing the micrometer, one division at a time, no
effect was produced, until the last millionth of an inch
5i of distance was traversed and absolute contact occurred
4! with the end of the bar, when the deflexion of the
needle of the galvanometer instantly detected the move-
ment. Repeated experiments showed this to be unerr-
ing in the result, and on placing the finger on the middle
of the bar, under the same circumstances as in the other
course of experiments, the expansion was instantly de-
tected by the deflexi©n of the galvanometer needle.
Tho delicacy of these experiments was so great as to
preclude the posaibilty of making them in a crowd, or
in a room with a varying temperature, therefore, al-
though the machine was destined for the National Ex-
hibition, its merits could not be appreciated or exhibited
there; it was announced, however, that probably another
opportunity would be afforded by Mr. Whitworth for the
exhibition of this beautiful instrument, whose results
were calculated to make great modifications in the cal-
culations of the changes of volumes of metals and other
substances under variation of temperature.
The paper read was "On the Demonstration of the
Rotation of the Earth, by means of Two Pendulums,"
by Mr. Homersham Cox, B.A.
rtesheenteeadrtbhy wthaes
The demonstration of thephreontaotmioennaopf
mechanical anpaupaelalryahmesedeeftothdeephenedaveoene.
Two
experi-
ments had, however, long been known, which demon-
atrated the fact that the earth revolved—the one, the
retardation of the pendulum by centrifugal force, a
question discussed by Newton, Huygens, and others;
the other, which was suggested by Newton, consisted in
dropping from a great height a ball, which, by the diur-
enateh. distance The
diur-
nal motion, was moved somewhat to the eastward.
The experiment had hitherto been performed with mie
pendulum, bat in the present instance two pendulums
apartwere need,te allowand woefr etsuspended
vibration e t
a osuffinie
f
weights were held together by a thread, which on being
burned released them, so that they were set vibrating,
initially, in the same vertical plane; consequently to the
eye of an observer situated in that piano the two pendu-
lum wires appeared coincident, one of them covering,
or eclipsing the other. In a short time, however, the
course of the two pendulums visibly altered. As their
planes of oscillation appeared to revolve the same way
thaes rapidity
manifested;
on the earth's surface, the wires no longer covered each
anifest withed; forwh as which
t
other, but appeared to separate and alternately to cross
each other.
The advantages of this mode of operating were, first,
h •planes revolved in the same
apparent direction their deviation the
w
arcs diverged from each other
twice as fast as either from initial "t* - and,
its position; _
secondly, the
apparent crossing and recrossing of the
wires constituted, to the n aired e ee, a much more dis-
tinct and palpable test of
the YI result than the apparent
motion referred to a plane beneath
The pendulum experiments one pendulum.
occupied_
that it was necessary to postpone the
so long a period
he paper ,
On some
New Mechanical Applicaticti of Vulcanised Caont-
chOnc,". by Mr. Btockedon,- amtil. the next Metting-,--on
TU,eSCISY eripingt May "I', when Mr. Leslie's paper