Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1896-06-07
SOME or THE GUESTS.
rnfnn ON Science nnl Inhustry.

DctailS or Herr BOelecheI lhbtlllou9
plan for insuring the nolselcss passage
Of trains over iron railway bridges have
been explained before the Verein fur
Observation-Disclosures. 1t consists OF a deck
ing Of 11-i-lnch planks between the
cross-girders. resting on S-inch timbers'
laid on the bottom hanges, and on these
planks double layer OF felt IS placed.
fixed to the vertical web OF the cross CIR
der; at the connections with the cir
der a timber-cOyered joint IS placed
on the felt, and two hooked bolts con-
meet the whole firmly 10 the bottom hange
Of the cross girder A depth Of four
inches OF Stag gravel covers the deck
ing and the latter is inclined toward the
centre Of the bridge. small tubes being
inserted through the decking connected
TO a suspended gutter for drainage pur-
poses. Great care is essential that the
felt be fixed accurately to the orders
and drainage tubes, and an arrangement
IS made by means Of which only water
and no gravel can pass through into the
gutter; a layer Of felt, well asphalted. is
also placed between the planks and the
timbers they rest upon, and the iron work
IN contact with decl,ings and ballast.
At the Geographical Congress in London
recently. several distinguished geograph-
ers expressed their opinion that the topO-
graphical map sheets issued by the United
States were the finest OF their class pro-
duced by any nation. AS illustrating the
scientific and mechanical completeness
characterlzing this work, IL is pointed out
that all water features are in blue. tho
hills are IN brown, contour lines show
Topographic forms and heights, while
Of m IiQrE
the next sheet IN the course is the came
basal map overprnted with the geological
cOlors, showing the surface, extent. and
position in the embraced area OF the
various rock formations. This sheet IS
entitled aerial geology. and the next map
Of the same area is known as economic
geology. and differs from the preceding
chiefly in the fact that The rock masses.
which are OF special Importance from
their yield of iron, gold. etc, are printed
In strong and the other rocks I'm sub
dued colors. These two maps show tho
surface only. and are succeeded by one
termed structure sections. representing
the under formations. perhaps half a
mile, more or less, indicating what has
been learned about that deeper portion
OF the earths crust. The sheet following
this is a diagram devoted 10 an exhibit.
Of c0lumnar sections. aud Illustrating the
geological age and thickness OF the rock
masses under investigation.
Among the results arrived at by the
committee appointed BY the American
Association Of Railway Superintendent.
for the purpose OF considering the
strength OF tlmbers for bridges and tres
ties. emphasis is laid on the fact
that variations I'm strength are general
~ directly proportionally 70 the density
or weight OF tie timber. and that struc-
lures should be, IN general, designed for
the strength of green or moderately sea-
soned timber, OF average quality. and not
for a high grade of well-seasoned ma
terial. age or use not destroying the
strength Of timber unless decay or sea-
son checking takes place 1t is found
that timber. unlike materials OF a more
HOMOGENEOUS nature. as iron or steel, has
no well-dehned limit Of elasticity; for.
as a rule, IL can be strained very near
to the breaking-point without serious in
Jury, which accounts for the continuous
use of many timber structures with the
material strained far beyond the usually
accepted safe limits; while. on the other
hand. sudden and frequently inexplicable
failures OF individual sticks at very low
limits are liable 10 occur. Knots, even
when sound and tight, are declared 20 be
one OF the most Objectionable features OF
timber. whether for beams or struts. The
full-size tests demonstrate not only that
beams break at knots. but that .nvari-
ably timber struts will fall, owing 60 the
proximity OF a knot, by reducing the
effective area Of the stick. and causing
curly and cross-grained fbres.