The Sun.
London, England, 1867-01-18 00:00:00

UNITED STATES POSTAL ARRANGEMENTS.

Mails for the United States are made up in London every
Saturday evening, Wednesday morning, and Wednesday
evening. Letters for the Saturday and Wednesday evening
mails must reach the General Post-office by 6 o'clock
p.m., and those of the Wednesday morning mails by 6
o'clock a.m. that day. Newspapers must always be posted
half an hour earlier. The Wednesday and Saturday's
mails are taken up at Queenstown, on the following day,
by the Liverpool steamers. The Wednesday morning
mails are taken by the Southampton steamers.
Mails from the United States are duo in London on
Mondays and Thursdays of each week.
Periodical works not of daily publication, issued in the
shape of pamphlets, may be sent to the United States,
California, and Oregon, by packet, at the following rates :
—Not exceeding 2 oz., id. ; above 2 oz., but not exceeding
3 oz., Gd.; above 3 oz., but not exceeding 4 oz., Bd. ; with an
addition of 2d. for every additional ounce up to 16
ounces, above which the privilege does not extend. At
the same rate of postage, auy pamphlet not weighing more
than 8 oz (even though it be not a periodical publication)
may be sent to the United States, California, and Oregon.
This postage is only the British portion, a further sum
being charged on delivery. The periodical works
or pamphlets must always be sent iu a cover open at the
ends (not more than ono being sent in a single cover), and
the postage must be prepaid. Other printed papers or
books (except those specified above), addressed to the
places above named, are liable to letter rate of postage.
There must be no writing, or other marks upon such
periodical works, pamphlets, &c., or upon the covers, ex-
cept the names and addresses of the persons to whom they
are sent; nor upon the covers must there be any printing,
except the names and addresses of the persons to whom
they are sent and the names and addresses of the senders
Any other writing, &c., will render the packotsliablo to
letter rates of postage.

THE PROPERTIES OF IRON AND STEEL.—In
considering the fitness of iron as a material for
ships and bridges, and particularly for the latter,
says Professor McGauley, one most dangerous
defect to which it is liable must he taken carefully
into account, namely, its tendency to crystallise,
and thus to lose a very large portion of its strength.
It appears from Mr. Fairbairn's experiments, that
with constant changes of load, or with the same
load, but with constant disturbance of the metallic
molecules, from vibration, fracture will, in time,
certainly ensue of itself. It has been ascertained
that an iron girder will break with about 400,000
changes of load, accompanied by vibrations ; a fact
which but too clearly shows that the spontaneous
destruction of our iron bridges is but a question of
time, and not even of a very long one. The ex-
planations of this very alarming fact, the danger
from which is, unfortunately, not even confined to
bridges, but extends to the axles of locom'otives and
carriages, and to the various portions of machinery
which from time to time so unexpectedly give way,
is found in the restoration to their primitive form
of the crystals which had been elongated and mutu-
ally entangled by the hammering to which the iron
is subjected during its manufacture. It might be
supposed that steel, from its tensile strength being
so much greater than that of iron, would be, in
every instance, far preferable to iron. Such, how-
ever, is not the case. If, for example, steel is
used in the formation of a girder, its thickness may
be much less than if iron were used. But this very
circumstance, as it is almost equally liable to oxida-
tion, causes its strength to be impaired with much
greater rapidity. Thus, a plate of iron half an
inch thick is much less weakened by oxidation to
the depth of the sixteenth of an inch than a plate of
steel which at first is only a quarter of an inch
thick. In the one case the strength of the plate is
diminished only to the extent of one-eighth ;
in the
other, with the same amount of oxidation, to the
extent of one-fowh hurtn
the latter. In the foritmwould be aureate
te
would stand, en i
give way. Again, it might be supposed that steel
would answer best where violent concussions are to
be withstood, and that, therefore, it would be an
excellent material for armour plates. The reverse
is, however, true. Steel is strong only when ex-
posed to a force that is slowly applied. A cannon-
ball which would cause only indentations in iron,
or, at the worst, merely pass through it, would dash
a plate of steel to pieces, dealing destruction, most
probably, to all those in its viciuity.—Pittsburgh
Mining Journal.