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Thomas Young is famous for his double slit experiment, but I can't seem to find his experimental setup (such as how is prepared the light before it went through the apparatus. Does anyone know his experimental arrangement? If so please can you describe it and provide a source (if possible). Also did Young publish any papers on his experiment?

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Young's original setup demonstrating interference of light was not double slit but sunbeam splitting with a single thin card. He presented a paper On the theory of Light and Color to the Royal Society in May 1801 published Proceedings of the Royal Society of London A 92 (1802) (see here and here), and in November 1803 gave a public talk Experimental Demonstration of the General Law of the Interference of Light published in Philosophical Transactions of the Royal Society of London, v.94 (1804) and reprinted in Morris Shamos, ed., Great Experiments in Physics, pp. 96-101, Holt Reinhart and Winston, New York, 1959.

Scheider describes the setup: "A narrow beam of sunlight was split with what Young described as "a slip of card, about one thirtieth of an inch in breadth (thickness)." The slip of card was held edgewise into the sunbeam, which was made to enter the room horizontally by means of a "looking glass" (mirror) and a tiny hole in a window shutter". The sunbeam had a diameter slightly greater than the thickness of the card. When the card was placed properly it split the beam into two slivers, one passing on each side of the slip of card". Young wrote:"I made a small hole in a window-shutter, and covered it with a piece of thick paper, which I perforated with a fine needle... It will not be denied by the most prejudiced, that the fringes are produced by the interference of two portions of light".

Even after the 1803 demonstration Brougham, a supporter of Newton's theory, called light interference "absurdity and one of the most incomprehensible suppositions that we remember to have met with in the history of human hypothesis", which might have inspired Young to modify the experiment. Back in 1802 he built water "ripple tank" with a more recognizable double slit setup to demonstrate interference of water waves, apparently inspired by Newton's double prism - double perforation setup for color splitting. The ripples were produced by a horizontally moved board, then passed through a single slit in the first shutter to create coherence, and then through two slits in the second shutter to produce the interference pattern, see here.

Around 1804 Young decided to convince the detractors by reproducing this exact setup with light. Results were published as Experiments and Calculations Relative to Physical Optics in the Proceedings A 94 (1804), and are reproduced in his 1807 Course of Lectures on Natural Philosophy and the Mechanical Arts, you can see the exact setup in its 1845 edition here.

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