When the results of Mr Young's labours became publicly known, a number of companies were started with the object of working on the lines laid down in his patent, and these not only in Great Britain but also in the United States, whither quantities of cannel coal were shipped from England and other parts to feed the retorts. In 1860, according to the statistics furnished, some seventy factories were established in the United States alone with the object of extracting oil from coal and other mineral sources, such as bituminous shale, etc. When Young's patent finally expired, a still greater impetus was given to its production, and the manufacture would probably have continued to develop were it not that attention had, two years previously, been forcibly turned to those discoveries of great stores of natural oil in existence beneath a comparatively thin crust of earth, and which, when bored into, spouted out to tremendous heights. The discovery of these oil-fountains checked for a time the development of the industry, but with the great production there has apparently been a greatly increased demand for it, and the British industry once again appears to thrive, until even bituminous shales have been brought under requisition for their contribution to the national wealth. Were it not for the nuisance and difficulty experienced in the proper cleaning and trimming of lamps, there seems no other reason why mineral oil should not in turn have superseded the use of gas, even as gas had, years before, superseded the expensive animal and vegetable oils which had formerly been in use. Although this great development in the use of mineral oils has taken place only within the last thirty years, it must not be thought that their use is altogether of modern invention. That they were not altogether unknown in the fifth century before Christ is a matter of certainty, and at the time when the Persian Empire was at the zenith of its glory, the fires in the temples of the fire-worshippers were undoubtedly kept fed by the natural petroleum which the districts around afforded. It is thought by some that the legend which speaks of the fire which came down from heaven, and which lit the altars of the Zoroastrians, may have had its origin in the discovery of a hitherto unknown petroleum spring. More recently, the remarks of Marco Polo in his account of his travels in A.D. 1260 and following years, are particularly interesting as showing that, even then, the use of mineral oil for various purposes was not altogether unknown. He says that on the north of Armenia the Greater is "Zorzania, in the confines of which a fountain is found, from which a liquor like oil flows, and though unprofitable for the seasoning of meat, yet is very fit for the supplying of lamps, and to anoint other things; and this natural oil flows constantly, and that in plenty enough to lade camels."