(Philadelphia), October 17, 1788. One-page autograph letter on bifolium, signed by Benjamin Franklin to John Vaughan. In part: "Inclos'd is a Power of Attorney from Dr. Ingenhousz to you & your Brothers, which I have just reciev'd. The original Certificates (of which here are authenticated Copies) are in the hands of your Brother Charles. We may confer on the Subject when you have a little Leisure, if you should want any further information..." Docketed on verso of integral leaf. Creasing from old folds. 8 1/8 x 6 3/8 in. (206 x 162 mm). In mat with a portrait of Franklin, and in frame, 14 3/8 x 18 1/4 in. (365 x 463 mm).

Benjamin Franklin writes to John Vaughan (1756-1841), son of Samuel Vaughan, Jr. (1720-1802), enclosing a power of attorney, authorizing John's father to act on behalf of Franklin’s friend, Dutch natural philosopher Jan Ingenhousz (1730-99), in his financial dispute with Philadelphia-born merchant and speculator Samuel Wharton (1732-1800).

In late 1780, Ingenhousz heavily invested in a scheme with Wharton involving the sale of textiles in America. Using the majority of his modest savings, Ingenhousz hoped to raise enough funds to leave his home in Vienna and move closer to Franklin, where they could engage in mutual scientific and philosophical pursuits. To his increasing frustration, and after years of hearing little to nothing of his investment, Ingenhousz asked Franklin to intercede on his behalf, believing he had been cheated out of a thousand pounds sterling by Wharton. Wharton's election to Congress in 1782 only increased Ingenhousz's anger, writing to Franklin of his disbelief that "a free and virtuous people should choose a man of such a black character [Wharton] as one of their Magistrates." (January 1, 1787). By early 1788, Franklin confirmed that Ingenhousz's money was lost, and urged him to come to America, as the only the way he could possibly recover it would be to sue Wharton in court. Unfortunately for Ingenhousz, he could not afford to make the trip, largely on account of his lost investment that had hobbled his finances throughout the 1780s. In early August 1788, Ingenhousz, with the help of Thomas Jefferson, composed the power of attorney that was originally included with this letter. According to Founders Online, that original document has not been located.

Ingenhousz, best known for the discovery of photosynthesis, befriended Franklin in London in the early 1760s. Although they only met on a few occasions in England over the course of their near 30-year friendship, they were frequent correspondents until Franklin's death in 1790, touching on topics that ranged from the philosophical, scientific, and the political. Born in Breda, Ingenhousz studied at the universities of Louvain and Leyden, and became attached to the Hapsburg court after inoculating the royal family against smallpox. He became acclaimed as a physician in Europe, and was one of the first natural philosophers to write on photosynthesis and electricity. In 1769, Franklin nominated him to the Royal Society, and Ingenhousz subsequently dedicated the first French edition of his Experiments Upon Vegetables (1780) to him. In 1786, Ingenhousz was elected a member of the American Philosophical Society.