The check-off system now in general use by the United Mine Workers, 730. — Why the operators have granted it: a precedent in the existing check-off for supplies, and in the presence of the check-weigh-man, 731. — History of the check-off system for union dues, 734. — Its main features, 735. — The unions' "card day" done away with, 737. — Effect of the check-off in strengthening the union, 738. — It acts to bring about virtually, tho not formally, the closed shop, 739.