The Sun.
London, England, 1841-04-12 00:00:00

TO THE EDITOR OF THE LIVERPOOL MERCURY.

" SIR—I know you are curious is matters of science,
and that you occasionally give insertion to questions
calculated to interest your readers, or excite their inge-
nuity. The question of the bursting of the Rupert's
drops, and the unannealed wine glass, I have, in my eye,
which you answered some time ago. Allow me, then,
to detail a curious accident which happened under my
owa hands, with a glass tube, and which has occurred
to several others, to whom I have mentioned it. Some
short time ago I procured a glass tube for the pur.
pose of constructing a barometer. After cleaning it well
with an iron wire, tipped with wash leather, I placed
it upon a table, and was astonished to find, in a
quarter of an hour, the tube broken into several pieces.
On mentioning it to a friend he immediately pronounced
it to be caused by the wire, as he had had a similar
accident. Not being satisfied that it could be preduued
by the wire, I placed another tube with a bit of wire
in it, and was surprised to find that, in a short time,
the cube broke into several pieces. I cannot account
for the phenomena, neither is the fact noticed in any
scientific treatises with which lam acquainted. Baro-
meter-makers seem to be aware of it, and never use
wire in cleaning their tubes.
Now, Sir, I shall feel much obliged if you, or any of
your scientific correspondents will give me an intelligible
explanation of the curious fact.—Yours, &c.,
W. A. S.

The phenomenon, which is the subject of our
Correspondent's letter, is familiar to the barometer
makers, who, in cleaning out the interior of the
tubes, take especial care that the iron wire em-
ployed for the purpose shall not touch the glass, as
the contact of the two substances is almost uni-
formly followed by a fracture of the glass, not im-
mediately, but after a short interval. This is one
of the most extraordinary circumstances of the
phenomenon ; as it is difficult, if not impossible,
w form any rational explanation of the secret mys-
terious operation which must be going on in the tube,
l tarry
There
tir:e why os f
to
does theb e ‘
an
it
effect,
te
in-
stantly
w between the moment of contact with the wire, and
the subsequent .fracture. If, as there is reason to
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ir
n e w
ith
tciol
en c!
Jul
adses,
pt
rhoed
u mcoemei t
he fa
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or intelligible cause. It seems
tiatio
ttkinditsan take place
adequate-ro
phenomenon is not altogether con-
fined to glass, but occasionally occurs in cast metal,
probably from its sudden cooling, or from not
having been Properly atmealed. However that
may be, it is a fact that the metal of which the
mirrors of reflecting telescopes are constructed, is
very apt to fly to pieces by the slightest scratch,
just like the barometer tubes, in consequence of
their coming in contact with the iron rod used to
clean out the inside.
n the reectilescope by
In our recent editorial article on the improve-
ments lately made `ye statedfl thatng, inte consequence
Lord Oxmantown, w
of the liability of the best metal to fly when even
slighly scratched in the operation of polishing, op-
ticians dared not meddle with -mirrors of large di-
mensions, on account of the risk, and that the con-
sequence was the substitution of an inferior metal,
which is not liable to become fractured. The
s the most suitable said to have suc-
ceeded nobleman whom
sori process
haveces s .
ou
rs t
working
named,
the mirrors
itseems,
i
as
to i
n obviate
constructingtliese risks,th
them
ttincl
of
metal, and of six feet diameter ; and, it is added,
that this is by no means the maximum, as the great
obstacle to the construction of much larger teles-
copes than have hitherto been practicable, appears
to have been surmounted ; and we may anticipate,
as the consequence
astonishing of the invention, the most
astronomical discoveries.
In conclusion,
we may observe, that the. pheno-
menon of the barometer tubes, noticed by our Cor-
respondent, is to be ascribed, no doubt, to their im-
perfect annealing, and that the remedy for the de-
fect would be that pointed out by Mr. Pellatt, of
London, at a late scientific meeting, from the report
of which we transcribe the following passage :
Mr. Pellatt recommended bodir4 as a sale and
good mode of annealing all kinds of glass ; in the ordi-
nary method of annealing, thick and thin ware is olteti
subjected to the Faille process, and remains in the leer
for the same period ; this would account for the supe-
rior duration of the thin tubes. He attributed the frac-
ture of the tubes to the tsnsion of the exterior coating,
and the vibration caused by the process of cleaning :
this effect was so well known that an old tube could
scarcely be sold, as it generally broke in cleaning.

BRUSSELS, APRIL 10.—The Mon tour pub-
lishes a long list of promotions in the a-my, on the occa-
sion of the birthday of the Duke of Brabant, who was six
years old yesterday. The public buildings were illuminated
in the evening.