Microscopes and Telescopes
By Rochelle Forrester
Ó All Rights Reserved
Publication Date 2006
The transparency of glass combined with the way in which light changes direction as it passes through one transparent medium to another, a phenomenon known as refraction, allows glass to be used for the purposes of magnification. When two (or with poorer results, one) lenses are used an object seen through those lenses is magnified. This is because the shape of the lenses causes light going through the lenses to converge at a particular focus or focal point in accordance with the laws of refraction. This focal point is different from the normal human focal point and allows the object to be magnified without blurring. The apparent size of an object increases as it is brought closer to the eye but if it is brought to close, blurring occurs. The blurring occurs because the lens in our eye cannot bend (or refract) light from an object enough to bring it into proper focus on the retina if it is to close. The lenses magnify by starting the refraction or bending process before the light enters the eye. This enables objects closer than the usual human focal point to be examined without losing focus. This was to result in the invention of glasses to correct bad vision and in the invention of the telescope and the microscope.
The particular shape of the lenses used in microscopes and telescopes can be worked out by using the law of refraction (known as Snel’s law after Willebrod Snel (1580-1626)) and trigonometry which was developed by the mathematician Rheticus (1514-76). An index of refraction establishes the angle at which light bends when going from one medium to another. When light passes from air through glass the refractive index is approximately 1.52. Armed with this knowledge it is possible to manufacture both microscopes and telescopes. Alternatively the earliest microscopes and telescopes may have been developed simply by experiment and observation.
The earliest lenses produced were eye glasses to correct defective vision and these were first developed in 13th century Italy. They were clearly developed from experimentation and observation without the benefit of Snel’s law or trigonometry. The earliest microscopes were invented by the Dutch spectacle makers Hans and Zacharus Janssen about 1590.
The social and cultural consequences of the invention of the microscope was the discovery of whole new worlds. An immense variety of micro-organisms were discovered, the leading microscopist being Antoni van Leeuwenhoek (1632-1723). Van Leeuwenhoek discovered protozoa in water, bacteria, blood corpuscles, capillaries, striations in skeletal muscle, the structure of nerves and spermatozoa. The microscope was soon to destroy the idea of spontaneous generation which held that many animals arose from spontaneous generation from particular environments. Mosquitoes came from stagnant water, bees from the carcasses of oxen and cattle, shellfish from mud and slime and snails from the putreification of fallen leaves. The work of van Leeuwenhoek and others showing the life style and sexual apparatus of such animals showed the idea of spontaneous generation was wrong, although it was not until the 19th century with the work of Louis Pasteur that the idea was finally put to an end.
The 17th and 18th century microscope had its thresholds so that while it could reveal certain things previously unknown, there was much it could not reveal. This lead to some theories that would not last due to more powerful microscopes proving them wrong. One such theory was that spermatozoa was the essential instrument of reproduction which fitted in with the belief in the pre-existence of organisms. Each new organism was considered to contain all the characteristics of all its predecessors. The spermatozoon was considered to be the means of transmission of all those characteristics to the new organism. This idea however failed to understand the role of the spermatozoon in fertilizing the egg and the contribution of the egg to the characteristics of the new organism. The idea however based on the information available to 17th and 18th century scientists was reasonable enough for the times. It was not until the 19th century when improved microscopes showed the spermatozoon and the egg contributed equally to the characteristics of the new organism. Microscopes of a certain power lead to certain information being available which lead to certain theories. Microscopes of a greater power would lead to additional information being provided which lead to different theories.
The telescope appears to have been invented by Hans Lipperhey, a spectacle maker in the Dutch town of Middelburg, who applied for a patent for it in 1608. Two other Dutchmen, Jacob Adriaenzoon and Sacharias Janssen also claimed to have invented the telescope, so a patent was refused. The Italian scientist Galileo heard about the Dutch invention and constructed his own telescope achieving a magnification of 20x, a better magnification than was to be achieved until 1630. Galileo’s telescope had two lenses, an objective lens at one end of the telescope and an ocular lens at the other end to which the eye was applied. The objective lens was a convergent or biconvex lens while the ocular lens was a divergent or biconcave lens. The effect of light passing through the lenses was to change the focal point of the light providing for a wider visual angle in which to view the object under observation. The telescope while operating a bit differently from a microscope, like the microscope, magnifies images through manipulating the focal point of light to create a wider visual angle in accordance with the laws of refraction.
Galileo, having created his telescope used it to look at the sky. He discovered a large number of previously unseen stars (the milky way), that the moon had an irregular surface, the sun was spotty and impure (sunspots), that Jupiter had four moons, there were rings around Saturn and the moon like phases of Venus. The observations were contrary to the astronometical theories of Ptolemy which had largely been accepted from classical times. Galileo’s observations, plus those of other scientists using even better telescopes, were to result in the ending of the Ptolemaic astronomy and its eventual replacement with the Newtonian system.
Prior to the invention of the telescope six planets (the Earth itself, Mercury, Venus, Mars, Jupiter and Saturn) were known to human beings and less than 5,000 stars were visible to the naked eye. The telescope lead to the discovery of Uranus in the 18th century, Neptune in the 19th century and Pluto in the 20th century. The invention of photography assisted the telescope in revealing the universe as it allowed objects to dim to be seen through a telescope to be photographed on a photographic plate over a long exposure time. The long exposure time allowed the photographic plate to record the existence of very faint objects as the plate will accumulate the effect of each photon hitting the plate over a period of time.
By the start of the 20th century it had become clear that our solar system was part of the Milky Way but it was not clear whether the Milky Way was the whole universe. It was not until the 1920’s when Edwin Hubble conclusively showed there were other galaxies and these galaxies were moving away from us with the furthest galaxies moving the fastest.
New forms of telescopes which detected different forms of electro-magnetic energy were developed. However most electro-magnetic energy other than visible light and radio waves is blocked by the earth’s atmosphere. The development of space rockets lead to telescopes being place in space, particularly the Hubble space telescope, to allow detection of electro-magnetic radiation in frequencies other than those of visible light and radio waves. Telescopes, using frequencies other than those of visible light, have detected radio wave evidence of planets in other solar systems, x-ray evidence of black holes, radio wave evidence of super nova explosions, and gamma ray and x–ray evidence of gamma rays originating from deepest space. Dark matter that could not be detected by any telescope operating on any electro-magnetic wave length was detected due to its gravitational effect on matter that was visible to telescopes.
If the telescope could not have been invented, for example if light did not refract when passing from one medium to another, then our view of the universe would have been quite different. It is possible we would have continued to believe, at least until the 20th century, that the sun and planets orbited the Earth and the universe consisted only of those objects that could be seen with the naked eye. Ever since the invention of the telescope at the start of the 17th century, telescopes had increased in power and the increasing power revealed different universes. Telescopes in the 17th century confirmed the Newtonian universe with the planets orbiting the sun in elliptical orbits while in the 20th century they showed the universe of General Relativity with planets orbiting the sun in circular orbits in curved space. As with the microscope instruments of a certain power revealed certain information that lead to certain theories. Instruments of greater power lead to additional information being provided which lead to different theories. The increasing power of microscopes and telescopes provided people with new information about for example micro-organisms and the orbits of planets, in an inevitable order leading to certain rational interpretations of the new information which produced theories using the new information. Given that humans are more or less rational beings, those theories followed inevitably from the information nature has made available through increasingly powerful microscopes and telescopes.