Article 1, Section 8, Clause 5
St. George Tucker, Blackstone's Commentaries 1:App. 261--621803
By the former articles of confederation it was agreed that the United States in congress assembled, should have the sole and exclusive right and power of regulating the alloy and value of coin struck by their own authority, or by that of the respective states; and fixing the standard of weights and measures throughout the United States. By the present constitution the respective states are interdicted from coining money. All the powers mentioned in this clause are branches of the royal prerogative in England, but are with much greater propriety vested in the legislative department by the federal constitution. The history of England affords numberless instances, where this prerogative has been exercised to the great oppression of the subject. The power of debasing the value of the coin, at pleasure, has in fact been frequently used as an expedient for raising a revenue, and is accordingly reckoned as one of the indirect modes of taxation, by the author of the treatise on political economy: for if the government gives coin of an inferior standard, for purer coin of the same weight, as is generally done in these cases; or if it receives more for the coin, than the value of the bullion, and the expence of the coinage, as is likewise frequently practised, the difference is an acquisition of revenue, paid by him who brings his bullion to the mint. According to the principles of our constitution, therefore, such a tax can not be imposed but by the representatives of the people.
Mr. Barrington, in his readings upon the English statutes, doubts whether the regulation of weights and measures be practicable, by law. He remarks, that in England it has been attempted by at least six different statutes, all of which have been ineffectual. He quotes an observation of Montesquieu's that it is the mark of a little mind in a legislature to attempt regulations of this kind. In England, perhaps, the attempt has not succeeded from some defect in the system. That proposed by Mr. Jefferson, when secretary of state, appears to be perfectly simple, and, I should apprehend, easily practicable: and the standard of measure, especially, may be obtained with a mathematical exactness sufficient for all the purposes of commerce, and even of arts and sciences.
It appears by the journals of the senate of the United States, March the 1st, 1791. "That a proposition had been made to the national assembly of France for obtaining a standard of measure, which shall at all times be invariable, and communicable to all nations, and at all times. That a similar proposition had been submitted to the British parliament: as the avowed object of these is to introduce an uniformity in the weights and measures of commercial nations; and as a coincidence of regulation by the government of the United States on so interesting a subject would be desirable, the senate resolved, that it would not be eligible at that time to introduce any alterations in the weights and measures of the United States."
The Founders' Constitution
Volume 3, Article 1, Section 8, Clause 5, Document 9
The University of Chicago Press
Tucker, St. George. Blackstone's Commentaries: With Notes of Reference to the Constitution and Laws of the Federal Government of the United States and of the Commonwealth of Virginia. 5 vols. Philadelphia, 1803. Reprint. South Hackensack, N.J.: Rothman Reprints, 1969.