Why did Young use a monochromatic source of light in his experiment?

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cuevamc · Accepted Answer

I think that the evidence is that at first Thomas Young did not use a monochromatic source (which he called homogeneous light) although of course using such a source would subsequently make the fringes easier to observe and obtain more accurate values for the wavelength of light.
He investigated of sound and then thin film interference and it was from these experiments (and using the data obtained by Newton) that he was able to estimate the wavelength of light.
He used sunlight to show diffraction due to a single narrow card as the Sun was a "handy" bright source of light although he was able to use candle light to observe the diffraction due to a strand of hair.
In his Lecture 39 "On the Nature of Light and Colours" Young gives evidence for particles which have rotational and undulational (vibrational) properties and he mentions a beam of homogeneous (monochromatic?) light falling on a screen in which there are two very small holes or slits which produce equally spaced dark stripes and the middle of the pattern always being bright.He then goes on to mention that for white (mixed as opposed to homogeneous) light the initial impression os of white light fringes but on closer inspection there was a "beautiful diversity of tints (colours)".
One of Young's biographers writes "Frustratingly, he never published a systematic experimental paper using the two =-slit arrangement . . . " so what he actually did and used can only be found in his lectures and his notebooks.
I have not been able to find a clear indication of what sources Young used to produce "homogeneous light"

Why did Young use a monochromatic source of light in his experiment?

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