Israel Jacobs, Esq.—Another brother of Mrs. Rittenhouse. ----- After experiencing the numerous and distressing privations incident to a nine months banishment from his home and separation from his family—during a period, too, of great calamity and suffering among his countrymen, Mr. Rittenhouse most joyfully returned to Philadelphia, soon after its abandonment by the hostile army; and there, once more, enjoyed the solace of a reunion with his wife and children; amidst whose tender embraces, and the mutual congratulations of his friends and fellow-citizens, especially of the returning exiles, he participated largely in those delightful sensations with which such an occasion, and such scenes, must have inspired a virtuous heart. In Philadelphia, Mr. Rittenhouse resumed the discharge of his official functions, as treasurer of the state; an office, in the execution of which there were very numerous and complicated duties, arising out of the novel system of finance and paper-credit, pursued by both the general and state governments during the war: consequently, his attention to this business engrossed so much of his time, as to leave him little leisure for pursuits more congenial to his mind. In a very short time after Mr. Rittenhouse’s return to Philadelphia he received a letter from Mr. Jefferson, congratulating him on that happy event: and expressing, in very forcible terms, the exalted sense that gentleman entertained of our Philosopher’s genius, talents, and usefulness. It indicates, also, the solicitude felt by its writer, lest the Orrery of Mr. Rittenhouse’s invention and construction, belonging to the College of Philadelphia, had been either removed or injured by the British forces, while they occupied that city. On this head, however, the apprehensions conceived by Mr. Jefferson proved to be groundless: for, not only was the Orrery not removed from its proper station; but, at the instance of the Rev. Dr. Smith, the provost of the College, the apartment in the College edifice which contained the invaluable machine, was closed up by order of Sir William Howe, to prevent its being injured; and no person was permitted to enter that apartment to view the Orrery, without the Provost’s consent; on which occasions he uniformly attended in person, with the keys kept in his possession. The means thus used, to secure from any injury property so inestimable to the friends of science, is a circumstance that certainly reflects much honour upon the parties by whom they were effected,—even though one of them was, at that time, necessarily viewed in the character of an “enemy.” But, in order that the reader may be enabled to form his own judgment, on Mr. Jefferson’s estimate of genius, and concerning the rank and privileges to which the distinguished writer conceives men of great philosophical talents are entitled, the letter, just referred to, is now presented to him: it is as follows.