I was prompted by a comment from Jim Collum in the Alternative Prints from Digital Negatives and Positives thread to unpack the phrase "the Chemical rays of light" used by Sir John Herschel in 1839 when he invented the word Photography and explained what he meant by it. First, part of the manuscript of Herschel's lectern notes at that momentous presentation:
"Photography" comes first and then the definition of the word is given next "or the application of the Chemical rays of light to the purpose of pictorial representation"
In 1839 no one knew what light was.
Long before, in 1690, Christiaan Huygens said light was travelling system of waves but Isaac Newton insisted that light was a stream of tiny particles. The argument lay unresolved.
In 1800 William Herschel (John Herschel's father) used a thermometer to measure the heat of various colours of a solar spectrum. Red was hotter than blue but to his surprise a region beyond the red, where nothing could be seen, was hotter still. There was something out there, perhaps the "heat rays of light", or maybe it was not light at all because there was nothing visible.
Inspired by William Herschel's example Johann Ritter in 1801 decided to explore the solar spectrum using the known property of light to darken silver chloride paper. Ritter found red light did not cause darkening but as he moved closer to blue the darkening increased. Again surprisingly, maximum darkening happened beyond the blue end of the spectrum. Could these be "chemical rays" that populated some of the visible spectrum but mainly lay beyond it? Using the reasonable supposition that if it couldn't be seen it wasn't light, the "stuff" beyond blue could be something entirely different and strange.
Thomas Young, the famous British polymath, observed, measured, and mathematically analysed optical diffraction effects in 1801. He concluded that light was indeed a wave and that he had actually determined wavelengths; accurately as it turned out. This unleashed a storm of controversy as the pre-eminence of British science was based on the majesty of Isaac Newton and it wouldn't do to prove Newton wrong on anything. Many thought that diffraction was merely the jostling of light particles and Young's wavelengths were merely the size of the particles themselves.
Sir John Herschel himself had found that an image perfectly focussed by eye would be slightly out of focus when recorded by a sensitive surface. There seemed to be a "visual focus" and a "chemical focus" quite close together and the difference between them varied a bit from lens to lens.
Less formal observations had already established that light had many other properties. Strong light would cause fabrics to fade but cause skin to darken. Light getting in the eyes would cause the sensation of sight. A lighted window would attract an indoor potplant to grow toward it.
So what was Sir John Herschel going to say in his lecture of March 14, 1839 in front of the Royal Society? His audience included top scientists, industrialists, millionaire aristocrats, and influential politicians some of whom rejected "infrared", "ultraviolet", "light waves", "diffraction", etc as non-Newtonian and an affront to British superiority.
Herschel trying to be as uncontroversial as possible said "the Chemical rays of light". He wasn't going to argue about what light was and which of it's "properties" was legitimate. He invoked only the property responsible for chemical changes; whatever that was.
A lot happened after 1839. James Clerk Maxwell in 1862 established light as an electromagnetic wave. Max Planck chopped light into quanta in 1900. Albert Einstein brought back light particles in 1905 and got a Nobel Prize for it. Richard Feynman the great American physicist formalised the quantisation of light in his 1965 Quantum Electrodynamics. And even more recently light has lost its individual identity by being combined with the weak nuclear force in Quantum Chromodynamics.
Given all that I say there is a strong case for identifying photography with its original principles. Doing so eliminates at a stroke all the controversies, contradictions, ambiguities, and ad hoc patch up jobs that try to shoehorn computer print-outs into photography, or digital negatives, or scanners, or film writers, or whatever is next in trying to get on the photography band wagon.
I believe that "the Chemical rays of light" is the best sword photography has, it is sharp, it cuts cleanly, and it should be swung freely at pretenders.
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Originally Posted by Maris Rusis
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