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Blocking occupies unused binding sites on the Western blot membrane. The primary antibody is applied, unbound material is washed away, and a labelled secondary antibody detects retained primary antibody. A fluorescence label emits detectable light after excitation; an enzyme-linked label can instead generate a colored product or light. Washing reduces background but does not prove that remaining binding is selective.

In the original experiment, blocking used excess protein. An anti-ribosome-protein serum followed by labelled secondary antibody produced colored or fluorescence bands; preimmune serum supplied comparison strips. The color readout was an enzyme reaction product, rather than a measurement of target enzyme activity. ^[ref]

An additive color display mixes separate red, green and blue emitters. A phosphor-converted white light-emitting diode converts some blue photons to longer-wavelength light in a phosphor, mixing it with unconverted blue to produce perceived white. Hiroshi Amano distinguishes display and phosphor-lighting applications.^[ref]

In a clear terrestrial atmosphere, Rayleigh scattering by air molecules redirects some sunlight toward an observer looking away from the Sun. Shorter wavelengths are preferentially scattered, enriching the scattered light in blue compared with the incoming sunlight. Along the longer atmospheric path to the low Sun, more short-wavelength light is removed from the direct beam, helping produce red sunsets. ^[ref].

Violet light has an even shorter wavelength than blue light, so the Rayleigh scattering wavelength dependence alone cannot predict the perceived sky color. The incoming solar optical spectrum and the eye's differing response to wavelengths both matter; human vision is less sensitive to violet than to blue. ^[ref]. Multiple scattering and other atmospheric particles also affect the observed sky. Cloud droplets are generally too large for this simple Rayleigh scattering model: Mie scattering describes spherical droplets, with much weaker visible wavelength selectivity, while repeated scattering helps make clouds appear white. ^[ref].

In August 1896, Pieter Zeeman observed broadened sodium spectral lines at Leiden, initially without resolved components. His lecture describes a slit and concave diffraction grating, then compares the broadening with the sodium doublet separation: about one thirtieth, roughly $0.2$ ångström. This supplied a spectral reference scale, not an absolute magnetic field calibration. Later cadmium photographs displayed resolved transverse triplets and axial doublets.^[ref]

The fuller report specifies a concave diffraction grating of ten-foot radius with 14,438 lines per inch, an adjustable slit and a micrometer eyepiece with vertical crosswire. Salt in a flame between electromagnet poles supplied the sodium spectral lines. Repeated switching broadened and restored them. To test changes in flame temperature or vapour density, Pieter Zeeman examined photon absorption through a heated porcelain tube with water-cooled glass windows. The arc lamp was displaced from the magnet and its light redirected by a mirror to avoid disturbing the arc. Rotating a narrower tube made the absorption spectral lines equally broad at different heights; the magnetic field still broadened their whole length.^[ref]

For the axial test, pierced electromagnet poles let the light travel along the magnetic field. A quarter-wave plate and polarizer selected one broadened edge; rotating the analyser by $90^{\circ }$ or reversing the magnet current exchanged the visible edge. The crosswire made its displacement detectable. This tested electromagnetic polarization as well as line width. For its rough estimate the report compared each side's widening with the sodium doublet separation, obtaining about one fortieth, and stated an approximate magnetic field intensity in historical units. These passages give no absolute field-calibration procedure; the inferred charge-to-mass ratio was explicitly a first approximation.^[ref]

Hendrik Antoon Lorentz's charged-oscillator theory connected the observed splitting to moving electric charge. In modern language, a line-position measurement needs a wavelength or frequency calibration and an independent magnetic field calibration before it determines a magnetic dipole moment. Resolving the individual components adds the transition information used in the worked example below.