MACADAM, John Loudoun, Scottish engineer, born in Ayr, Scotland, 21 September, 1756; died in Moffat, Dumfriesshire, 26 November, 1836. On the death of his father he was sent to his uncle, William Macadam, who had settled as a merchant in New York city. The nephew was placed in a counting-house, became a successful merchant, and, espousing the royal cause in 1775, was agent for the sale of prizes at the port of New York. In 1783 he was compelled to return to Scotland, and purchased an estate in Ayrshire. He began in 1810 to experiment on the construction of roads, and, in spite of great opposition, succeeded in carrying into effect the system that is known by his name. This system depends on Mr. Macadam's discovery that small angular fragments of stone will coalesce or bind into a compact mass under pressure, and his principle that the efficiency of a road is in proportion to the thoroughness with which water is excluded from the soil on which it rests. Mr. Macadam gave his services and advice without charge on all occasions, and declined many offers of remunerative offices abroad. In 1825 he was voted £6,000 by parliament toward repaying the expenses that he had incurred in introducing his system, and he declined the honor of knighthood, which was subsequently bestowed on his son James. Mr. Macadam married Margaret Nicoll, of Islip, L. I., during his stay in New York, and after his death in 1827 took for his second wife Charlotte, sister of Bishop de Lancey. He published "Practical Essay on the Scientific Repair and Preservation of Public Roads" (London, 1819); "Remarks on the Present State of Roadmaking" (1820); and "Observations on Roads" (1822).