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Living on the Air 269 as to be negligible. Suddenly the value of the agent became appreciated. Railways were laid down tap- ping the deposits, which were worked feverishly. By the early ’seventies the world realised that it could not do without the article, the result being that the annual export of the fertiliser increased by leaps and bounds, rising from 200,000 to 1,400,000 tons in thirty years. And of this huge total 75 per cent., or over 1,000,000 tons, are used for feeding wheat- raising lands for the express purpose of getting absolutely the uttermost bushel per acre. The value of Chilian saltpetre as a wheat stimu- lant was convincingly demonstrated by Sir John Lawes and Sir Henry Gilbert, the results of whose studies were communicated to the world by Sir William Crookes. At Rothamstead a field was selected and sown year after year for thirteen years with wheat, no fertiliser whatever being used. These conditions, it may be remarked, are comparable with those exist- ing to-day in the United States, Canada, and other new wheat-growing territories. And, strange to say, the annual yield was comparable with what the American and Canadian farmers obtain, averaging 12 bushels per acre for the thirteen years. The soil was then dressed with Chilian saltpetre and grown with wheat under these conditions for another thirteen consecu- tive years, the fertiliser being applied every year. The results were astonishing ; the yield of wheat per acre jumped from 12 bushels to 36I bushels. In other words, the stimulation of the soil increased the yield by 300 per cent. ! If what was done at Rotham- stead were repeated in those new territories, the annual yield of wheat throughout the world, allowing