Meantime the wax candle and the Argand oil lamp held their own bravely. The whaling fleets, long after gas came into use, were one of the greatest sources of our national wealth. To New Bedford, Massachusetts, alone, some three or four hundred ships brought their whale and sperm oil, spermaceti, and whalebone; and at one time that port was accounted the richest city in the United States in proportion to its population. The ship-owners and refiners of that whaling metropolis were slow to believe that their monopoly could ever be threatened by newer sources of illumination; but gas had become available in the cities, and coal-oil and petroleum were now added to the list of illuminating materials. The American whaling fleet, which at the time of Edison's birth mustered over seven hundred sail, had dwindled probably to a bare tenth when he took up the problem of illumination; and the competition of oil from the ground with oil from the sea, and with coal-gas, had made the artificial production of light cheaper than ever before, when up to the middle of the century it had remained one of the heaviest items of domestic expense. Moreover, just about the time that Edison took up incandescent lighting, water-gas was being introduced on a large scale as a commercial illuminant that could be produced at a much lower cost than coal-gas. Throughout the first half of the nineteenth century the search for a practical electric light was almost wholly in the direction of employing methods analogous to those already familiar; in other words, obtaining the illumination from the actual consumption of the light-giving material. In the third quarter of the century these methods were brought to practicality, but all may be referred back to the brilliant demonstrations of Sir Humphry Davy at the Royal Institution, circa 1809-10, when, with the current from a battery of two thousand cells, he produced an intense voltaic arc between the points of consuming sticks of charcoal. For more than thirty years the arc light remained an expensive laboratory experiment; but the coming of the dynamo placed that illuminant on a commercial basis. The mere fact that electrical energy from the least expensive chemical battery using up zinc and acids costs twenty times as much as that from a dynamo--driven by steam-engine--is in itself enough to explain why so many of the electric arts lingered in embryo after their fundamental principles had been discovered. Here is seen also further proof of the great truth that one invention often waits for another.