10th May 1773. ‘Let there be Light, and Sound!
The seven Colour Frequencies and seven Sound Frequencies are used by the eyes, ears and via artistic endeavour, in music and painting.
Today in 1773 at the age of 35, William Herschel purchased a copy of James Ferguson’s Astronomy. A lucky purchase as he went on to design telescopes, observed the nebula of Orion, and discovered Uranus.(1)
It was William Herschel’s work with prisms which led to his discovery that different colours have different wavelengths and he found that varying amounts of heat was given off, with short wavelength blue, being the hottest.
The frequency of the wavelength determines the colour along the spectrum from red to violet.
Sunlight is a spectrum of different wavelengths, similar to a radio station broadcasting along the whole waveband of 400-700m.
It contains various colours each with its own brightness or intensity. Rainbows or prisms send these component colours in different directions making them visible at different angles.
Intensity depends on varying circumstances, the eye is more sensitive to green and yellow than red, for at night we can hardly see red, thus we have yellow sodium lights, not red neon.
In pigments we notice red more, so red for danger, which could be biological; blood is red!
When all visible frequencies are present equally, they are perceived as White Light, the spectrum is then Flat Line. This concept also refers to other wave phenomena such as sound, when it has its frequencies mixed.(2)
So this mixture of audible frequencies distributed over the audio spectrum, results in White Noise, which is often used in the medical condition of Tinnitus.
Herschel’s work led to his discovery in 1800 of Infra-Red-Rays, which lie between visible red in the light wavelengths, and microwaves.
About this time Thomas Young, showed that three colours: red, blue and green can be combined to give appearance of white light or any of the spectral colours and many besides which raises the question about the colour brown.(3)
Indigo as a colour was first recorded in 1289 and considered for long as one of the colours of the rainbow (optical spectrum) and placed in the electromagnetic spectrum between 420 and 450 nanometres in the wavelength, between blue and violet.(4)
So three cheers for Herschel and Young who shed the light on light.
(1) He also discovered Infrared Radiation and was elected to the Royal Society.
(2) This also relates to vibration.
(3) Brown covers a wide range in the visual spectrum and is long wavelength and low frequency. It is of low intensity, being a tertiary colour made up of red, orange and yellow. The colour is described as a composite adjective, so we get reddish brown, tan brown etc.
(4) Electromagnetic waves oscillate electrical and magnetic fields through space. Its spectrum from left to right shows: radio waves having the longest waves and lowest frequency. Next comes microwaves.
Then Infrared, before the narrow band of visible light. Then ultra-violet rays (UV) before the narrow region of X-rays, and finally gamma rays.
Ref: physics classroom.com/class/light.
Ref: theinquirer.net/light-split-into-spectrum. Pic. Ref.