The reduction in the cost of helium is really one of the most important developments of this war. By removing the fire risk from airships we can safely use these craft for aërial cruises or for quick long-distance travel over land and sea. For, even in time of peace, sailing under millions of cubic feet of hydrogen is a serious matter. Although no incendiary bullets are to be feared, there is always the danger of setting fire to the gas within the exhaust of the engines. Engines have had to be hung in cars well below the balloon proper. But with helium in the gas-bags the engines can be placed inside the balloon envelop and the propellers can operate on the center line of the car. In the case of one Zeppelin, the hydrogen was set on fire by an electric spark produced by friction on the fabric of one of the gas-bags, and so even with the engine exhausts properly screened there is danger. The helium airship, however, would be perfectly safe from fire and passengers could smoke on deck or in their cabins within the balloon itself without any more fear of fire than they would have on shipboard. Wonderful possibilities have been opened by the production of helium on a large and economical scale, and the airship seems destined to play an important part in transportation very soon. As this book is going to press, we learn of enormous dirigibles about to be built in England for passenger service, which will have half again as great a lifting-power as the largest Zeppelins. The final chapter of the story of dirigibles is yet to be written, but in concluding this chapter it is interesting to note that the world's greatest aëronautic expert got his first inspiration from America and finally that America has now furnished the one element which was lacking to make the dirigible balloon a real success. CHAPTER IX GETTING THE RANGE Every person with a good pair of eyes in his head is a range-finder. He may not know it, but he is, just the same, and the way to prove it is to try a little range-finding on a small scale.