#4. Sunday-school Extension.#--Sunday-schools soon became very popular, and spread over Great Britain and into Europe. Sunday-schools are known to have existed in the United States as early as 1786, and probably much earlier than that (even in 1674). They found congenial soil in the Western Hemisphere, and multiplied rapidly. There are now more than a quarter of a million Sunday-schools in the world, enrolling more than twenty-five millions of people. More than one-half of this vast army is in North America. #5. The Sunday School Union of London.#--This organization was effected in 1803 in Surrey Chapel, London, and is the oldest expression of organized Sunday-school work. It is local only in name. Its auxiliaries are to be found in all parts of the United Kingdom, Continental Europe and the various dependencies of Great Britain. It holds valuable properties in London, conducts an extensive printing establishment, and maintains a large corps of workers as secretaries, colporteurs, etc., not only in Great Britain but on the Continent, in India and elsewhere. #6. The American Sunday School Union.#--The earliest Sunday-school organizations in North America were a Sunday School Union in New York City in 1816, another in Boston the same year, and still another in Philadelphia in 1817. These were combined in 1824 into a national society known as The American Sunday School Union. This society, through its large corps of missionaries, plants new Sunday-schools, especially on the frontier. It conducts a large publishing establishment at its headquarters in Philadelphia, and has done and is doing a great work. #7. The National Sunday School Convention.#--The first national interdenominational convention in the United States was held in the city of New York in 1832. Delegates were present from fourteen states and four territories. A second convention was held in the city of Philadelphia, the following year, 1833. Not until 1859 was the third convention held, and this one also in the city of Philadelphia. In 1869, in Newark, N. J., may be said to have begun the present series of great conventions in our country, for they have been held triennially from that time until the present. The fourth and last strictly national convention was held in the city of Indianapolis in 1872. Here the International System of Uniform Lessons had its birth. The International Lessons went into use January, 1873. They are selected by a committee appointed by the International Convention, co-operating with a similar committee appointed by the Sunday School Union of London. It was decided that the next convention should be international in character, and include the Dominion of Canada. #8. International Sunday School Movement.#--International conventions have been held triennially since 1875.