SIR,--I am indebted to you for the communication of the prospectus of a work embracing the history of civilized man, political and moral, from the great change produced in his condition by the extension of the feudal system over Europe through all the successive effects of the revival of letters, the invention of printing, that of the compass, the enlargement of science, and the revolutionary spirit, religious and civil, generated by that. It presents a vast anatomy of fact and reflection, which if duly filled up would offer to the human mind a wonderful mass for contemplation. Your letter does not ascertain whether this work is already executed, or only meditated; but it excites a great desire to see it completed, and a confidence that the author of the analysis is best able to develop the profound views there only sketched. It would be a library in itself, and to our country particularly desirable and valuable, if executed in the genuine republican principles of our constitution. The only orthodox object of the institution of government is to secure the greatest degree of happiness possible to the general mass of those associated under it. The events which this work proposes to embrace will establish the fact that unless the mass retains sufficient control over those intrusted with the powers of their government, these will be perverted to their own oppression, and to the perpetuation of wealth and power in the individuals and their families selected for the trust. Whether our constitution has hit on the exact degree of control necessary, is yet under experiment; and it is a most encouraging reflection that distance and other difficulties securing us against the brigand governments of Europe, in the safe enjoyment of our farms and firesides, the experiment stands a better chance of being satisfactorily made here than on any occasion yet presented by history. To promote, therefore, unanimity and perseverance in this great enterprise, to disdain despair, encourage trial, and nourish hope, are the worthiest objects of every political and philanthropic work; and that this would be the necessary result of that which you have delineated, the facts it will review, and the just reflections arising out of them, will sufficiently answer. I hope, therefore, that it is not _in petto_ merely, but already completed; and that my fellow citizens, warned in it of the rocks and shoals on which other political associations have been wrecked, will be able to direct theirs with a better knowledge of the dangers in its way. The enlargement of your observations on the subjects of natural history, alluded to in your letter, cannot fail to add to our lights respecting them, and will therefore ever be a welcome present to every friend of science. Accept, I pray you, the assurance of my great esteem and respect. TO THE HONORABLE MR. NELSON. MONTICELLO, April 2d, 1812.