We had to cut a new flange disk for the broken wheel, and to prevent the flanges from splitting off again we nailed a batten across the inner face of each wheel extending down to the very edge of the flange disk.  This batten was fastened on across the grain.  When everything was completed the car was started down the track empty to see if it would keep the rails.  It went beautifully as far as the bridge, but was too light to run much beyond.  The next time we loaded it up with stones and had the pleasure of watching it sail down hill, across the bridge and vanish out of sight around the shore of Kite Island.  That was demonstration enough.  We knew it would carry us safely and it did.  The next time we tried it four of us piled into the small car, and in a moment we were off on a most thrilling ride, which ended right in front of the log cabin, where the car came to a sudden stop after riding off the end of the rails and plowing through the sand for a short space.

CHAPTER XXV.

THE CANTILEVER BRIDGE.

There is one more piece of work done by our society which yet remains to be described, and that is the cantilever bridge.  This we all voted to be the greatest of our achievements on the island.  To be sure, it was Uncle Ed’s design, but I think we justly deserve credit for the masterful way in which it was erected.  In our search for types of bridges before building the king post bridge, we came across a simple cantilever bridge that didn’t look very difficult to construct.  To be sure, none of us knew a thing about stresses and strains, and ingenious though we were, Bill realized that the task of designing a cantilever bridge was far beyond him.  Nevertheless, we were sure we could build one if only we had a good set of plans.  A letter was therefore mailed to Uncle Ed, asking him for the required details.  The answer came promptly from Western Australia, asking us to send him the exact width of the water we wished to span, the depth of the water, the distance from the top of one bank to the top of the other, and the exact height of the banks above water level.  We decided we would build the bridge across the mouth of the lagoon.  The distance here between the two banks measured a little over 60 feet.  The banks were very precipitous, and rose 13-1/2 feet above the level of the water.  All these details, together with soundings of the bottom, all the way across, were sent to Uncle Ed, and on the day after our railway was completed quite a bulky package was received in answer.  It contained complete directions for building the bridge of wooden frames, which were so designed that they needed merely to be hooked together to form the bridge, though to make the structure perfectly safe Uncle Ed cautioned us to tie the frames together wherever they met.

I am half afraid to tell my readers how to build this bridge, as it required the utmost care, and had to be built just so to avoid disaster.  Bridge building is a serious business, and I would not advise anyone to attempt building this, of all bridges, who does not propose to follow instructions implicitly.  Uncle Ed told us that if we built it properly, and with sound timbers, we would find the bridge strong enough to support a dozen boys, but he warned us not to crowd more than that number on it.