(How and when) Spectral Physics (was born) or first fragment of a Lover's Dictionary on...
William Blake, ‘To Venetian Artists’
... in the beginning of the year 1666 (at which time I applyed my self to the grinding of Optick glasses of other figures then Sphericall) I procured me a triangular glasse Prisme to try therewith the celebrated phænomena of colours. And in order thereto having darkned my chamber & made a small hole in my window-shuts to let in a convenient quantity of the sun's light, I placed my Prism at its entrance that it might be thereby refracted to the opposite wall. It was at first a very pleasing divertisement to view the vivid & intense colours produced thereby; but after a while applying my selfe to consider them more circumspectly, I became surprized to see them in an oblong form, which according to the received lawes of refraction I expected should have been circular.
They were terminated at the sides with streight lines, but at the ends the decay of light was so graduall that it was difficult to determine justly what was their figure, yet they seemed semicircular.
Comparing the length of this Coloured Spectrum with its bredth I found it about five times greater, a disproportion soe extravagant that it excited me to a more then ordinary curiosity of examining from whence it might proceed; I could scarce think that the various thicknesse of the glasse, or the termination with shaddow or darknesse could have any influence on light to produce such an effect, yet I thought it not amisse to examine first those circumstances, & soe tryed what would happen by transmitting light through parts of the glasse of divers thicknesses, or through holes in the window of divers bignesses, or by setting the Prism without, so that the light might passe through it & bee refracted before it was terminated by the hole: but I found none of those circumstances materiall. The fashion of the colours was in all these cases the same.
Isaac NewtonTrinity Coll Cambridge. Feb. 6. 1671/2
I envision spectral physics as a scientific endeavour based on a set of experimental and conceptual spectroscopes to scrutinise and merge in a coherent picture the macroscopic and microscopic features of the phenomenological world physicists probe thanks to telescopes, high energy accelerators, extremely low temperature devices, very high magnetic fields ... etc, and confront with heuristic tools like quantum mechanics, thermal physics or general relativity while mathematicians formalise the computations confirmed by nature with theories like Euclidean geometry, calculus, Fourier analysis, Riemannian manifolds and their noncommutative extensions with a proper spectral calculus.