a third, still thicker
*
Plate 2, No. 1
(slightly cropped to square; identifying number removed from lower left)
The first of eight photographs (on two plates) illustrating
Herbert Stansfield (1872-1960). “Observations and Photographs of Black and Grey Soap Films.” Proceedings of the Royal Society of London : Series A, Containing papers of a mathematical and physical character. vol. 77 ( January 3, 1906) : 314-323
Cornell copy, digitized January 3, 2014
The full paper is also made available as a separate pdf by the Royal Society via archive.org. The images are stunning when encountered in their primarily textual context.
In No. 1, the dark area in the middle of the film at the top is the thinnest of the greys; the next thicker one can be seen at each side; and, in the original, it is possible to distinguish a third, still thicker, stretching across the film below the other two... p 317
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tags: black; fine shadings; grays; thin films
H. Stansfield, “Observations and Photographs of Black and Grey Soap Films.” (1906)