Numerous measurements have been made of the wavelengths of the brightest.
A body which absorbs all radiations of all wavelengths would be called a "perfectly black body."
It is seen that as the coupling k becomes small these two wavelengths coalesce into one single wave length.
The enclosed area for each temperature represents the total emission of energy for that temperature, the abscissae are the wavelengths, and the ordinates the corresponding intensities of emission for that wave-length.
If a collective system be corrected for the axis point for a definite wave-length, then, on account of the greater dispersion in the negative components - the flint glasses; - over-correction will arise for the shorter wavelengths (this being the error of the negative components), and under-correction for the longer wave-lengths (the error of crown glass lenses preponderating in the red).
In another direction, making a small angle with the last, such that the projection of AB upon it amounts to a few wavelengths, it is easy to see that the mode of interference is the same as if there were no ruling.
We may therefore put y=a sin -T (x - e) +b sin (x - f)+c sin 6 (x - g) +&c. (21) where the terms may be infinite in number, but always have wavelengths submultiples of the original or fundamental wave-length A.