In the 5th century BCE, Empedocles believed that Aphrodite lit the fire which shone out from the eye making sight possible but he realized that this must interacted with light from the sun or a flame in some way.
About 300 BCE, Euclid questioned the idea that light travelled from the eye to a star and then back again as this would be possible only if light travelled infinitely fast. He studied the laws of reflection mathematically and argued that light travelled in straight lines.
In 55 BCE, Lucretius, suggested that the light and heat of the sun were transmitted by minute atoms which were propelled at great speed.
In 1010 CE, Alhazen (Ibn al-Haytham), influenced by Ptolemy's work, insisted that vision was the result of rays entering the eye. He analyzed these rays geometrically and wrote the Book of Optics which was disseminated through out Western Europe by a Latin translation.
Avicenna (980-1037) noted that, if the perception of light was caused by the emission of some sort of particles emitted from a luminous source, the speed of light must be finite. Al-Bīrūnī (973-1048) agreed and pointing out that the speed of light was much greater than the speed of sound as lightening could be seen long before thunder was heard. During the 11th century, Abu 'Abd Allah Muhammad ibn Ma'udh used the angle of the sun at sunrise and sunset to estimate the height of the atmospheric moisture responsible for the refraction of the sun's rays. Late in the 13th century, Qutb al-Din al-Shirazi (1236–1311) and his student Kamāl al-Dīn al-Fārisī were among the first to give the correct explanations for the rainbow phenomenon.
In England, Roger Bacon (1214–1294) wrote about the importance of light, citing recently translated works about optics, including those of Grosseteste, Alhacen, Aristotle, Avicenna, Averroes, Euclid, al-Kindi, Ptolemy, Tideus, and Constantine the African.
In the Netherlands, in 1609, Antonie van Leeuwenhoek discovered that certain shaped lenses increased an image's size in 1609 and, with Dutch spectacle makers Zaccharias Janssen and Hans Lipperhey and Galileo Galilei, invented the compound microscope. It was similar to the recently invented telescopes but used an objective lens near the specimen with an eyepiece. It permitted scientists like Van Leeuwenhoek and Robert Hooke, to observe single celled bacteria, suspended in water, for the first time, thus founding the study of waterborne diseases and the science of microbiology.
Other naturalists in Italy, the Netherlands and England began using them to study biology but it was 1644 before Giambattista Odierna published the first details of the microscopic anatomy of organic tissue in L'occhio della mosca (The Fly's Eye) and Marcello Malpighi, began his analysis of biological structures with the lungs. The 1665 publication of Robert Hooke's Micrographia, with its impressive illustrations, aroused huge interest.
Antonie van Leeuwenhoek made significant discoveries with a simple single lens microscope able to magnify up to 300 times. He sandwiched a very small glass ball lens between the holes in two metal plates, riveted together, and with a specimen mounted on a screw adjusted needle. He re-discovered red blood cells (after Jan Swammerdam) and spermatozoa, and helped popularize the use of microscopes to examine biological material. The performance of early microscopes depended on the ability to focus light on the specimen and the quality of the condenser and the objective lenses to capture the light from the specimen and form an image. Early microscopes were limited until this principle was understood and electric lamps became available.
In 1893 August, Köhler overcame the limited contrast and resolution imposed by early techniques as he devised ways to uniformly illuminate the sample and obtain maximum resolution. In 1953, Frits Zernike discovered phase contrast and, in 1955, Georges Nomarski invented differential interference contrast illumination, which permitted better imaging of unstained, transparent samples.
Early glass makers had noticed that blobs of glass produced a range of colours, as well as magnifying objects, so early glass production was used for jewellery and other ornaments.
This is caused by the different frequencies of visible light travelling at slightly different speeds and thus having slightly different refractive indexes. So, sunlight is split into a spectrum when passing through rain and other transparent material like lenses where the different colours do not focus at the same point.
Through most of 1603, Johannes Kepler (1571–1630) puzzled over the optical effects of eclipses particularly the red colour of a total lunar eclipse and on January 1, 1604, he published his findings. He described the inverse-square law governing the intensity of light, reflection by flat and curved mirrors, and principles of pinhole cameras, as well as the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies. Oddly, he did not mention refraction.
In 1608, experiments in the spectacle-making centres of the Netherlands, led to the invention of the refracting telescope. Galileo greatly improved upon these designs the following year.
In 1621, Willebrord Snellius (1580–1626) described the mathematical law of refraction, (Snell's law). Later, René Descartes (1596–1650) used this to show that the angle between the edge of the rainbow and the rainbow's centre was 42°.
Isaac Newton (1643–1727) demonstrated that a triangular glass prism would split sunlight (which is white) into a spectrum of rainbow colours, and that a similar prism could recombine the multicoloured spectrum back into white light. He also separated one of the coloured beams and directed it at various objects to demonstrate that it did not change its colour whether it was reflected, scattered or again refracted; it remained the same colour and could not be split further. He concluded that the colour of objects is not generated by the object but by their absorption of some of the colours in white light and the reflection of other colours. He also realized that in any refracting telescope, a simple lens would refract each colour at a slightly different angle so that each colour would have a slightly different focal point resulting in chromatic aberration.
Curved mirrors did not have this problem so he ground and polished his own mirrors for a reflecting telescope which he demonstrated in 1671. He knew that neither a spherical lens nor a spherical mirror provided a perfectly sharp focus as the spherical aberration was greater with larger lenses or mirrors but he made a spherical mirror for the reflecting telescope because it was easier to make than a parabolic mirror that would have provided a sharper focus.
Samuel Klingenstierna (1698 – 1765) a Swedish professor at Uppsala University from 1728, was the first to point out errors in Newton's theories of refraction and, in 1760, he developed the theory behind the invention of the Achromatic Telescope. This made possible large reflecting telescopes up to the 40 foot focal length, 120-centimetre (47 in) diameter telescope made by Herschel and installed at the British Greenwich observatory in 1789.
Almost all of the major telescopes used in astronomy research today are reflectors because they allow very large diameter objectives.
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Atoms & Light
Non-FictionIn 1657, Otto von Guericke pumped the air from two hemispheres and eight horses could not pull them apart. Amontons found a volume of air shrank as the temperature fell and realized the it would become zero. In 1774, Joseph Priestley isolated oxyge...
