I have recd. your favor of Sepr 10. with a Copy of the printed documents on the subject of the slave trade.1 The mask of humane professions covering an indifference in some & a repugnance in others to its effectual abolition, is as obvious as it is disgusting. G. B. alone, whatever may be her motives, seems to have the object really at heart. It is curious at the same time to observe her experiment for bringing about a change in the law of Nations by denominating the trade piracy, without the universal consent wch. she held essential to the Code of the Armed Neutrality dissented from solely by herself. Her Cabinet is chargeable with a like inconsistency, in its readiness to interpose between the Allied powers & Spanish Ama. & its scruples to do so agst. the invasion of Spain herself. Nor is it easy to reconcile the advances made to you in behalf of our Southern Neighbors, with a disrelish of your proposition that their Independence be immediately acknowledged, a right to do which appears to have been publickly asserted. In point of mere policy it excites surprize, that if the Brit: Govt. dreads the foreseen extension of the views of the Holy Alliance to Span: Ama. in the event of success in the invasion of Spain, it did not arrest the invasion, as it might have done, by a like interposition with that which is to stifle the projected resubjugation of her former Colonies. It can excite no surprize, indeed, that our co-operation should be courted in measures that may lead to war; it being manifest that in such an issue, G. B. would be under the dilemma, of seeing our neutral commerce & navigation aggrandized at the expence of hers, or of adding us to her enemies by renewing her paper blockades, and other maritime provocations. May it not be hoped that a foresight of this dilemma will be a permanent check to her warlike propensity?

But whatever may be the motives or the management of the B. Govt. I can not pause on the question whether we ought to join her in defeating the efforts of the Holy Alliance to restore our Independent Neighbors to the condition of Spanish Provinces. Our principles & our sympathies, the stand we have taken in their behalf, the deep interest we have in friendly relations with them, and even our security agst. the Great Powers, who having conspired agst. natural rights & reforms must point their most envenomed wrath agst. the U.S. who have given the most formidable example of them; all concur in enjoining on us a prompt acceptance of the invitation to a communion of counsels and if necessary of arms in so righteous & glorious a cause. Instead of holding back, I should be disposed rather to invite, in turn, the B. Govt. to apply at least “the small effort” of Mr. Canning2 to the case of the French Invasion of Spain, and even to extend it to that of the Greeks. The good that wd. result to the world from such an invitation if accepted, and the honor to our Country even if declined, outweigh the sacrifices that would be required, or the risks that wd. be incurred. With the British fleets & fiscal resources associated with our own we should be safe agst. the rest of the world, and at liberty to pursue whatever course might be prescribed by a just estimate of our moral & political obligations.

You ask my view of the claim of the U.S. to the navigation of the St. Laurence thro’ the Brit: territory, and my recollection of the grounds on which they claimed that of the Mississippi thro’ Spanish territory. On the latter point I may refer to a Report of a Committee of the Revolutionary Congress in 1780 (see vol. 2. p 326 of the secret Journals now in print3 which I presume you have) in which among other things the right of the U.S. is argumentatively touched on; and to the extract now inclosed from a letter I wrote to Mr. Jefferson then at Paris in the year 1784.4 in which there is a glance at the cases having more or less of analogy to that of the Mississippi. It being more easy to obtain by another hand the extract as it stands than to separate the irrelevant matter by my own, I must trust to that apology for obtruding a perusal of the latter. At the dates referred to the navigation of the Mississippi was a cardinal object of national policy: and Virga. feeling a particular interest in it thro’ Kentucky then a part of the State, the claim was warmly espoused by her public Councils of which I was a member at the last date and one of her Delegates to Congress at the first.

As a question turning on natural right & public law I think the navigation of the St. Laurence a fair claim for the U.S.

Rivers were given for the use of those inhabiting the Country of which they make a part: and a primary use of the navigable ones is that of external commerce. Again, the public good of Nations is the object of the Law of Nations, as that of individuals composing the same nation, is of municipal law. This principle limits the rights of ownership in the one case as well as in the other; and all that can be required in either is that compensation be made for individual sacrifices for the general benefit. This is what is done in the case of roads & the right of way under a municipal jurisdiction, and is admitted to be reasonable, in the form of tolls, where a foreign passage takes place thro’ a channel protected & kept in repair by those holding its shores. Vattel allows a right even in Armies marching for the destructive purposes of war, to pass thro’ a neutral Country, with due precautions.5 How much stronger the claim for the beneficial privileges of commerce?

In applying these principles it is doubtless proper to compare the general advantage with the particular inconvenience and and to require a sufficient preponderance of the former. But was there ever a case in which the preponderance was greater than that of the Mississippi; and the view of it might be strengthened by supposing an occupancy of its mouth limited to a few acres only: and by adding to the former territory of the U.S. the vast acquisition lately made on the waters of that River. The case of the St. Laurence is not equally striking, but it is only in comparison with the most striking of all cases, that its magnitude is diminished to the eye. The portion of the U.S. connected with the River & the inland seas, through which it communicates with the Ocean, forms a world of itself, and after every deduction suggested by the artificial channels which may be substituted for the natural, they will have a sufficient interest in the natural to justify their claim and merit their attention. It will be a question with some perhaps whether the use of the River by Citizens of the U.S. will not be attended with facilities for smuggling, and a danger of collisions with a friendly power, which render its attainment little desireable. But if any considerable body6 Citizens feel a material interest in trading thro’ that channel, and there be a public right to it, the Govt. will feel much delicacy in forbearing to contend for it.

How far it may be expedient to appeal from the transitory calculations to the permanent policy of G.B. in relation to Canada, as was done with respect to Spain & Louisiana, you can best judge. I have noticed allusions in Parliament to the considerations recommending an alienation of the Province;7 and it is very possible that they may be felt by the Govt. But it may well be expected that the solid interest of the Nation will be overruled by the respect for popular prejudices, & by the colonial pasturage for hungry favorites. It is very certain that Canada is not desireable to the U.S as an enlargement of Domain. It could be useful to them only, as shutting a wide door to smuggling, as cutting off a pernicious influence on our Savage neighbours, and as removing a serious danger of collisions with a friendly power.

Having made these observations as due to your request I must not decline saying, that whatever just bearing any of them may have on the point of right in the case of the St. Laurence, I consider the moment for asserting it not the most propitious if a harmony of views be attainable with the B. Govt. on the great subject of Spanish America, to say nothing of other subjects in principle akin to it. I doubt not however that eno’ will be left to your discretion, and that there will be more than eno’ of that so to manage the discussion as to prevent an interference of one object with the other.

Just as the above was closed the fall of Cadiz & the Cortes are confirmed to us. What next is the question. Every great event in the present state of the world may be pregnant with a greater. As the Holy Alliance will premise negociation & terror to force agst. the new States South of us, it is to be hoped they will not be left in the dark as to the ultimate views of G. B in their favor. To conceal these wd. be to betray them as Spain has been betrayd.