Having made up the debit account, we should be able to set against it the compensations in naval protection, bounties,[138] drawbacks, British capital, and long credits, in developing colonial agriculture and commerce.[139] Unfortunately there does not exist any history of the commerce of the American colonies, from the Commonwealth to 1774, as affected by navigation laws, acts of trade, and revenue measures. No one who has read the twenty-nine acts which comprise this legislation will recommend their perusal to another; for, apart from their volume, the construction of these acts is difficult,—difficult even to trained lawyers like John Adams, whose business it was to advise clients in respect to them.[140] Nor have special students, like Bancroft, stated their effect with exact precision, as in respect to the Act of 1663;[141] and notably in respect to the Townshend Act of 1767,[142] where his error amounts to a perversion of its meaning. Palfrey has been more successful, though not entirely free from error.[143] The author of the _Development of Constitutional Liberty_,[144] a work of uncommon research and ability, reads the act of 1672 as though it prohibited the carrying of fish from Massachusetts to Rhode Island except by the way of England, failing to notice that it was not one of the "enumerated articles", or that even those could pass directly from colony to colony upon payment, at the place of export, of duties equivalent to those laid upon their importation to England. To give a monographic treatment to the subject would require familiarity with the construction of statutes, and exact information not only of the shifting conditions of colonial trade, but of the evasions which called forth supplemental acts, or constructions of existing acts by the Board of Trade.[145] In Burke's _Account of the European Settlements in America_[146] much may be found respecting colonial products and commerce, and especially those of New England (in ch. vii.), which leaves little to be desired concerning the sources of her wealth, and the complaints of British merchants of the methods by which it had been acquired. But I have found nowhere else so full and clear an account of the course of trade of Boston at the time of the Revolution, and the effect upon it of the enforcement of the navigation laws and acts of trade in 1770, as in an anonymous pamphlet entitled _Observations of the Merchants at Boston in N. E. upon Several Acts of Parliament, 1770_.[147] An essential part of this history is that which relates to the medium of exchange, and to the attempts of Parliament to regulate the issue of paper money as a legal tender in the interests of British merchants.[148]