It will be recalled that we pointed out that the greatest danger to people riding in dirigibles was the possibility of heat expanding and exploding the hydrogen gas. One of the first airships to experience this fate simply passed through a cloud into the hot sun, whose rays expanded and exploded the gas, blowing the airship and its crew into smithereens before they could open the gauges and release the pressure. The same thing may have caused the explosion of the German dirigible L-2, which killed its crew of twenty-five; and the American airship _Akron_, which blew up, destroying Vaniman and his companions. The substitution of helium entirely eliminates that danger and makes it possible to carry heating devices for the comfort of passengers in high altitudes where it is so cold. Of course, the lifting power of helium was known to students of aerostatics before the war, but the mechanical difficulties and cost involved in producing this gas on an industrial basis were so great that it would hardly pay to produce it for commercial purposes. Indeed, the largest amount of helium in any one container up to the beginning of 1918 was five cubic feet, and it cost between fifteen hundred and six thousand dollars, whereas under the new system it is expected that one thousand cubic feet can be produced for one hundred dollars! In war, however, cost is nothing—results are everything. As there was a possibility that helium might be one of the chief factors in winning the war, the joint Army and Navy Board on Rigid Airships in August, 1917, provided the Bureau of Mines with the requisite funds to do the necessary experiment work. This, however, is not the time or the place to go into a detailed description of this wonderful gas or how it was obtained, further than to state that apparatus had to be designed on entirely new lines for the liquefaction of nitrogen into natural gases, at temperatures as low as -317 degrees Fahrenheit; that the natural gas of Kansas, Oklahoma, Texas, and Ontario contains 1 per cent of helium; that a $900,000 building was constructed for the Navy Department at Fort Worth, Texas, and a ten-inch pipe-line ninety-four miles long was laid, at a cost of more than a million dollars, from the wells at Petrolia, Texas, for supplying the plant with natural gas; and that the first production of it was in operation April 1, 1918.