In June 1867, James Glaisher, an English astronomer and meteorologists, and an avid balloonist, was floating over Paris in a balloon when he entered a region of dense cloud:
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Suddenly, whilst we are thus suspended in the misty air, we hear an admirable concert of instrumental music, which seems to come from the cloud itself and from a distance of a few yards only from us. Our eyes endeavour to penetrate the depths of white, homogeneous, nebulous matter which surrounds us in every direction. We listen with no little astonishment to the sounds of the mysterious orchestra.
Source: amusingplanet.com