The San Francisco call., 1907-02-17

enough to reach between the supports
These supports. may be simply, Of
inch board. as at \ in the drawing, as
wide at the top as the bridge board
which is shown at b.
I'm the center OF the board, or a. foot
from each end. fasten couple OF sticks
G about three quarters of an inch wide
with stick connecting tliem across the
top making Il square frame over the
middle of the bridge, considerably Higher
than the cars or vehicles that you intend
to run over the bridge. or under this
frame If you put a track across for your
car line-Q have been telling the boys
how to make railroad and a street car
line)''--he explained TO his listeners you
want to remember that the track will
addfsome height to your cars, too.
About f--e inches from each end of
the bridge or a little less as may suit
your fancy, fasten Two other frame
works similarly made as at ID, the pieces
E. connecting across the top as in the
center frame. The end frames d, how
eyer, are slanted off toward the ends
of the foot-board a little, the slant in
each case being the same. OF course.
I'VE now cut strips of tin about half
an inch wide-and il yoN haven't any
handy YOU can pick them I'D almost for
1Vbthtib 0uQLt ttlt AIluliileL ia any ltH
shop-and measure off their length The
pieces (b) on either end and side reach
ing from the ends of the foot-board to
the top Of the first frame d must, of
course, be of equal length.
The pieces (c) running from the GEN.
ter frame to the ends of the frames D
above are somewhat longer but also OF
equal length on either side.
Where these pieces join the wooden
frames and the foot-board they are
fastened by shngle nails (n) driven
through holes in the tin into the frame
in the positions shown.
while the thin board itself which
forms the floor OF the bridge would alone
hold very little weight yet with these
'trusses' added as l have described the
strength is enormously Increased and
you will be surprised how great a load
tho bridge will hold.
IL you have no road under the bridge.
or if the piers A at the ends are high
enough you may t. the bridge upside
down and have the truss work under
meath the floor. leaving more room on
the bridge itself.
IF the bridge has pretty wide span
you can easily put up a support in the
center and makes turn bridge like those
you see on the rivers where the boats
have to pass through"
Here Jack laid aside the drawings he
had been showing and picked up another
set Of sketches at his side. like those at
the bottom of this page.
This shows how to make a tunnel, .,
he continued, that I'm going to tell the
boys about, too, in connection with tho
railroad. There's not much TO that
either.
You take a piece of inch board as
long as your tunnel is TO be, or a little
longer, and as wide. The arch part *
made by melting up q lot Of old tomato
cans in a fire and then bending the tin
into the right arch shape and tacking Il
to the board, which is shown at r in
Fig. 1, by brads or tacks at +: the tins
overlapping q little at each joint
''Of course. if you are to use the tunnel
for railway you will need to Law the
track on the board before you put the
tin roof of the tunnel on, fastening the
tracks directly to the board without
ties
''At each end of the tunnel is a board
II, in Fig. I, cut In the shape shown.
with the door part at o, cut so the tin
tunnel will fit just inside its curve, where
1t can be fastened by means OF tacks or
brads through holes (p).
You dig the hole where YOU want the
tunnel to be, set it in its place and then
cover it up again while the boards Ii