The exclusive privilege of an incorporated trade necessarily restrains the competition, in the town where it is established, to those who are free of the trade. To have served an apprenticeship in the town, under a master properly qualified, is commonly the necessary requisite for obtaining this freedom. The bye-laws of the corporation regulate sometimes the number of apprentices which any master is allowed to have, and almost always the number of years which each apprentice is obliged to serve. The intention of both regulations is to restrain the competition to a much smaller number than might otherwise be disposed to enter into the trade. The limitation of the number of apprentices restrains it directly. A long term of apprenticeship restrains it more indirectly, but as effectually, by increasing the expense of education.