_From a letter of the 19th of April._--That Mr Dana has communicated to Count de Vergennes his appointment, and requested his advice concerning the conduct, which circumstances demanded on his part. That it gave the Count great pleasure to observe this proof of the confidence, which Congress and their Ministers reposed in the friendship and advice of his Court. That the Count informed Mr Dana, that he would run the risk of exposing his person, and the dignity of the United States, if he assumed any character whatsoever in Russia, while the Empress had not acknowledged the independence of the United States, and expected to act the part of a mediatrix, which demanded the most perfect impartiality. That Mr Dana felt the propriety of the observation; and proposed to the Count, that he should appear in Russia in the character of a common traveller, keep his commission a secret, and avoid with the greatest care to speak of business, unless requested so to do by the Russian Ministry. That the Count fully approved of this prudent scheme; and apprized Mr Dana of all the difficulties he would meet with. He had him recommended to the Marquis de Verac, Envoy Extraordinary at the Court of Petersburg; and the Chevalier de la Luzerne is directed to assure Congress, that the Marquis de Verac would do all in his power for Mr Dana's best reception, and with pleasure assist him with his counsels, as often as he should have recourse to them. That the Marquis de Verac had communicated to the Russian Ministry the resolution of Congress, concerning the principle of the declaration made by the Empress of Russia to the belligerent powers. That this Envoy informs the Count de Vergennes, that the contents of this resolution had afforded great satisfaction to Count Panin, Minister of Foreign Affairs, who intended to submit it without delay to the perusal of the Empress. That the Marquis de Verac did not doubt, but that she would be pleased with the readiness of Congress to adopt that principle; and that correspondent resolutions will have been taken respecting the navigation of the neutrals.