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through the narrowest of slits, 1
 

image

ex Professor Piazzi Smyth, Colour, in Practical Astronomy, Spectroscopically Examined. in Transactions of the Royal Society of Edinburgh 28 (1879): 779-843 (this being p 791, as scanned)

Why?
Was looking for some colour amongst Transactions ca 1850-1900 with which to punctuate these dry, insipid pages, and landed monochromatically here. Charles Piazzi Smyth (1819-1900 *) was for many years Astronomer Royal for Scotland, and did also measure every surface, dimension, and aspect of the Great Pyramid.

…so as to allow, as one example only, the solar red-prominences to be plainly and broadly observed, without the usual spectroscopic draw-back of having to look at them through the narrowest of slits.
*

30 October 2012
tags: colour; Piazzi Smyth; practical astronomy; words