Newton’s research in
the field of refractive index showed
that a prism can
split white light into a spectrum of
colors. Light rays are refracted by
the "thick" side
of a prism and thus separated according to
the wavelength. In the conventional optical glasses
the blue light rays are refracted more
strongly the long-wavelength
red ones, though with the diffraction grating
the red light waves are deflected more. The physical reason for this
is dependent on
the wavelength of the light refractive index.

In this  experiment, using a
prism a narrow beam of white light is pulled apart  to form a colored band of
lights - the
spectrum.