Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent; the birefringence is quantified as the maximum difference between refractive indices exhibited by the material. Crystals with non-cubic crystal structures are birefringent, as are plastics under mechanical stress. Birefringence is responsible for the phenomenon of double refraction whereby a ray of light, when incident upon a birefringent material, is split by polarization into two rays taking different paths; this effect was first described by the Danish scientist Rasmus Bartholin in 1669, who observed it in calcite, a crystal having one of the strongest birefringences. However it was not until the 19th century that Augustin-Jean Fresnel described the phenomenon in terms of polarization, understanding light as a wave with field components in transverse polarizations. A mathematical description of wave propagation in a birefringent medium is presented below.
Following is a qualitative explanation of the phenomenon. The simplest type of birefringence is described as uniaxial, meaning that there is a single direction governing the optical anisotropy whereas all directions perpendicular to it are optically equivalent, thus rotating the material around this axis does not change its optical behavior. This special direction is known as the optic axis of the material. Light propagating parallel to the optic axis is governed by a refractive index no. Light whose polarization is in the direction of the optic axis sees an optical index ne. For any ray direction there is a linear polarization direction perpendicular to the optic axis, this is called an ordinary ray. However, for ray directions not parallel to the optic axis, the polarization direction perpendicular to the ordinary ray's polarization will be in the direction of the optic axis, this is called an extraordinary ray. I.e. when unpolarized light enters an uniaxial birefringent material it is split into two beams travelling different directions.
The ordinary ray will always experience a refractive index of no, whereas the refractive index of the extraordinary ray will be in between no and ne, depending on the ray direction as described by the index ellipsoid. The magnitude of the difference is quantified by the birefringence: Δ n = n e − n o; the propagation of the ordinary ray is described by no as if there were no birefringence involved. However the extraordinary ray, as its name suggests, propagates unlike any wave in a homogenous optical material, its refraction at a surface can be understood using the effective refractive index. However it is in fact an inhomogeneous wave whose power flow is not in the direction of the wave vector; this causes an additional shift in that beam when launched at normal incidence, as is popularly observed using a crystal of calcite as photographed above. Rotating the calcite crystal will cause one of the two images, that of the extraordinary ray, to rotate around that of the ordinary ray, which remains fixed.
When the light propagates either along or orthogonal to the optic axis, such a lateral shift does not occur. In the first case, both polarizations see the same effective refractive index, so there is no extraordinary ray. In the second case the extraordinary ray propagates at a different phase velocity but is not an inhomogeneous wave. A crystal with its optic axis in this orientation, parallel to the optical surface, may be used to create a waveplate, in which there is no distortion of the image but an intentional modification of the state of polarization of the incident wave. For instance, a quarter-wave plate is used to create circular polarization from a linearly polarized source; the case of so-called biaxial crystals is more complex. These are characterized by three refractive indices corresponding to three principal axes of the crystal. For most ray directions, both polarizations would be classified as extraordinary rays but with different effective refractive indices. Being extraordinary waves, the direction of power flow is not identical to the direction of the wave vector in either case.
The two refractive indices can be determined using the index ellipsoids for given directions of the polarization. Note that for biaxial crystals the index ellipsoid will not be an ellipsoid of revolution but is described by three unequal principle refractive indices nα, nβ and nγ, thus there is no axis. Although there is no axis of symmetry, there are two optical axes or binormals which are defined as directions along which light may propagate without birefringence, i.e. directions along which the wavelength is independent of polarization. For this reason, birefringent materials with three distinct refractive indices are called biaxial. Additionally, there are two distinct axes known as optical ray axes or biradials along which the group velocity of the light is independent of polarization; when an arbitrary beam of light strikes the surface of a b
A mirror image is a reflected duplication of an object that appears identical, but is reversed in the direction perpendicular to the mirror surface. As an optical effect it results from reflection off of substances such as water, it is a concept in geometry and can be used as a conceptualization process for 3-D structures. In geometry, the mirror image of an object or two-dimensional figure is the virtual image formed by reflection in a plane mirror. Two-dimensional mirror images can be seen in the reflections of mirrors or other reflecting surfaces, or on a printed surface seen inside-out. If we look at an object, two-dimensional and turn it towards a mirror, the object turns through an angle of 180º and we see a left-right reversal in the mirror. In this example, it is the change in orientation rather than the mirror itself that causes the observed reversal. Another example is when we stand with our backs to the mirror and face an object that's in front of the mirror. We compare the object with its reflection by turning ourselves 180º, towards the mirror.
Again we perceive a left-right reversal due to a change in orientation. So, in these examples the mirror does not cause the observed reversals; the concept of reflection can be extended to three-dimensional objects, including the inside parts if they are not transparent. The term relates to structural as well as visual aspects. A three-dimensional object is reversed in the direction perpendicular to the mirror surface. In physics, mirror images are investigated in the subject called geometrical optics. In chemistry, two versions of a molecule, one a "mirror image" of the other, are called enantiomers if they are not "superposable" on each other; that is an example of chirality. In general, an object and its mirror image are called enantiomorphs. If a point of an object has coordinates the image of this point has coordinates, thus reflection is a reversal of the coordinate axis perpendicular to the mirror's surface. Although a plane mirror reverses an object only in the direction normal to the mirror surface, there is a perception of a left-right reversal.
Hence, the reversal is called "lateral inversion". The perception of a left-right reversal is because the left and right of an object are defined by its perceived top and front, but there is still some debate about the explanation amongst psychologists; the psychology of the perceived left-right reversal is discussed in "Much ado about mirrors" by Professor Michael Corballis. Reflection in a mirror does result in a change in chirality, more from a right-handed to a left-handed coordinate system; as a consequence, if one looks in a mirror and lets two axes coincide with those in the mirror this gives a reversal of the third axis. If a person stands side-on to a mirror and right will be reversed directly by the mirror, because the person's left-right axis is normal to the mirror plane. However, it's important to understand that there are always only two enantiomorphs, the object and its image. Therefore, no matter how the object is oriented towards the mirror, all the resulting images are fundamentally identical.
In the picture of the mountain reflected in the lake, the reversal normal to the reflecting surface is obvious. Notice that there is no obvious front-back or left-right of the mountain. In the example of the urn and mirror, the urn is symmetrical front-back. Thus, no obvious reversal of any sort can be seen in the mirror image of the urn. A mirror image appears more three-dimensional if the observer moves, or if the image is viewed using binocular vision; this is because the relative position of objects changes as the observer's perspective changes, or is differently viewed with each eye. Looking through a mirror from different positions is like looking at the 3D mirror image of space. A mirror does not just produce an image of. A mirror hanging on the wall makes the room brighter because additional light sources appear in the mirror image. However, the appearance of additional light does not violate the conservation of energy principle, because some light no longer reaches behind the mirror, as the mirror re-directs the light energy.
In terms of the light distribution, the virtual mirror image has the same appearance and the same effect as a real, symmetrically arranged half-space behind a window. Shadows may extend from the mirror into the halfspace before it, vice versa. In mirror writing a text is deliberately displayed in mirror image, in order to be read through a mirror. For example, emergency vehicles such as ambulances or fire engines use mirror images in order to be read from a driver's rear-view mirror; some movie theaters take advantage of mirror writing in a Rear Window Captioning System used to assist individuals with heari
In chemistry, a coordination complex consists of a central atom or ion, metallic and is called the coordination centre, a surrounding array of bound molecules or ions, that are in turn known as ligands or complexing agents. Many metal-containing compounds those of transition metals, are coordination complexes. A coordination complex whose centre is a metal atom is called a metal complex. Coordination complexes are so pervasive that their structures and reactions are described in many ways, sometimes confusingly; the atom within a ligand, bonded to the central metal atom or ion is called the donor atom. In a typical complex, a metal ion is bonded to several donor atoms, which can be the same or different. A polydentate ligand is a molecule or ion that bonds to the central atom through several of the ligand's atoms; these complexes are called chelate complexes. The central atom or ion, together with all ligands, comprise the coordination sphere; the central atoms or ion and the donor atoms comprise the first coordination sphere.
Coordination refers to the "coordinate covalent bonds" between the central atom. A complex implied a reversible association of molecules, atoms, or ions through such weak chemical bonds; as applied to coordination chemistry, this meaning has evolved. Some metal complexes are formed irreversibly and many are bound together by bonds that are quite strong; the number of donor atoms attached to the central atom or ion is called the coordination number. The most common coordination numbers are 2, 4, 6. A hydrated ion is one kind of a complex ion, a species formed between a central metal ion and one or more surrounding ligands, molecules or ions that contain at least one lone pair of electrons. If all the ligands are monodentate the number of donor atoms equals the number of ligands. For example, the cobalt hexahydrate ion or the hexaaquacobalt ion 2+ is a hydrated-complex ion that consists of six water molecules attached to a metal ion Co; the oxidation state and the coordination number reflect the number of bonds formed between the metal ion and the ligands in the complex ion.
However, the coordination number of Pt2+2 is 4 since it has two bidentate ligands, which contain four donor atoms in total. Any donor atom will give a pair of electrons. There are some donor groups which can offer more than one pair of electrons; such are called polydentate. In some cases an atom or a group offers a pair of electrons to two similar or different central metal atoms or acceptors—by division of the electron pair—into a three-center two-electron bond; these are called bridging ligands. Coordination complexes have been known since the beginning of modern chemistry. Early well-known coordination complexes include dyes such as Prussian blue, their properties were first well understood in the late 1800s, following the 1869 work of Christian Wilhelm Blomstrand. Blomstrand developed; the theory claimed that the reason coordination complexes form is because in solution, ions would be bound via ammonia chains. He compared this effect to the way. Following this theory, Danish scientist Sophus Mads Jørgensen made improvements to it.
In his version of the theory, Jørgensen claimed that when a molecule dissociates in a solution there were two possible outcomes: the ions would bind via the ammonia chains Blomstrand had described or the ions would bind directly to the metal. It was not until 1893 that the most accepted version of the theory today was published by Alfred Werner. Werner’s work included two important changes to the Blomstrand theory; the first was that Werner described the two different ion possibilities in terms of location in the coordination sphere. He claimed that if the ions were to form a chain this would occur outside of the coordination sphere while the ions that bound directly to the metal would do so within the coordination sphere. In one of Werner’s most important discoveries however he disproved the majority of the chain theory. Werner was able to discover the spatial arrangements of the ligands that were involved in the formation of the complex hexacoordinate cobalt, his theory allows one to understand the difference between a coordinated ligand and a charge balancing ion in a compound, for example the chloride ion in the cobaltammine chlorides and to explain many of the inexplicable isomers.
In 1914, Werner first resolved the coordination complex, called hexol, into optical isomers, overthrowing the theory that only carbon compounds could possess chirality. The ions or molecules surrounding the central atom are called ligands. Ligands are bound to the central atom by a coordinate covalent bond, are said to be coordinated to the atom. There are organic ligands such as alkenes whose pi bonds can coordinate to empty metal orbitals. An example is ethene in the complex known as Zeise's salt, K+−. In coordination chemistry, a structure is first described by its coordination number, the number of ligands attached to the metal. One can count the ligands attached, but sometimes the counting can become ambiguous. Coordination numbers are between two and nine, but large numbers of ligands are not uncommon for the lanthanides and actinides; the number of bonds
In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electric field of the wave has a constant magnitude but its direction rotates with time at a steady rate in a plane perpendicular to the direction of the wave. In electrodynamics the strength and direction of an electric field is defined by its electric field vector. In the case of a circularly polarized wave, as seen in the accompanying animation, the tip of the electric field vector, at a given point in space, describes a circle as time progresses. At any instant of time, the electric field vector of the wave describes a helix along the direction of propagation. A circularly polarized wave can be in one of two possible states, right circular polarization in which the electric field vector rotates in a right-hand sense with respect to the direction of propagation, left circular polarization in which the vector rotates in a left-hand sense. Circular polarization is a limiting case of the more general condition of elliptical polarization.
The other special case is the easier-to-understand linear polarization. The phenomenon of polarization arises as a consequence of the fact that light behaves as a two-dimensional transverse wave. On the right is an illustration of the electric field vectors of a circularly polarized electromagnetic wave; the electric field vectors have a constant magnitude but their direction changes in a rotary manner. Given that this is a plane wave, each vector represents the magnitude and direction of the electric field for an entire plane, perpendicular to the axis. Given that this is a circularly polarized plane wave, these vectors indicate that the electric field, from plane to plane, has a constant strength while its direction rotates. Refer to these two images in the plane wave article to better appreciate this; this light is considered to be right-hand, clockwise circularly polarized. Since this is an electromagnetic wave each electric field vector has a corresponding, but not illustrated, magnetic field vector, at a right angle to the electric field vector and proportional in magnitude to it.
As a result, the magnetic field vectors would trace out a second helix. Circular polarization is encountered in the field of optics and in this section, the electromagnetic wave will be referred to as light; the nature of circular polarization and its relationship to other polarizations is understood by thinking of the electric field as being divided into two components which are at right angles to each other. Refer to the second illustration on the right; the vertical component and its corresponding plane are illustrated in blue while the horizontal component and its corresponding plane are illustrated in green. Notice that the rightward horizontal component leads the vertical component by one quarter of a wavelength, it is this quadrature phase relationship which creates the helix and causes the points of maximum magnitude of the vertical component to correspond with the points of zero magnitude of the horizontal component, vice versa. The result of this alignment is that there are select vectors, corresponding to the helix, which match the maxima of the vertical and horizontal components.
To appreciate how this quadrature phase shift corresponds to an electric field that rotates while maintaining a constant magnitude, imagine a dot traveling clockwise in a circle. Consider how the vertical and horizontal displacements of the dot, relative to the center of the circle, vary sinusoidally in time and are out of phase by one quarter of a cycle; the displacements are said to be out of phase by one quarter of a cycle because the horizontal maximum displacement is reached one quarter of a cycle before the vertical maximum displacement is reached. Now referring again to the illustration, imagine the center of the circle just described, traveling along the axis from the front to the back; the circling dot will trace out a helix with the displacement toward our viewing left, leading the vertical displacement. Just as the horizontal and vertical displacements of the rotating dot are out of phase by one quarter of a cycle in time, the magnitude of the horizontal and vertical components of the electric field are out of phase by one quarter of a wavelength.
The next pair of illustrations is that of left-handed, counter-clockwise circularly polarized light when viewed by the receiver. Because it is left-handed, the rightward horizontal component is now lagging the vertical component by one quarter of a wavelength rather than leading it. To convert a given handedness of polarized light to the other handedness one can use a half-waveplate. A half-waveplate shifts a given linear component of light one half of a wavelength relative to its orthogonal linear component; the handedness of polarized light is reversed when it is reflected off a surface at normal incidence. Upon such reflection, the rotation of the plane of polarization of the reflected light is identical to that of the incident field. However, with propagation now in the opposite direction, the same rotation direction that would be described as "right handed" for the incident beam, is "left-handed" for propagation in the reverse direction, vice versa. Aside from the reversal of handedness, the ellipticity of polarization is preserved.
Note that this principle only holds for light reflected at normal incidence. For instance, right circularly polarized light reflected from a dielectric surface at grazing incidence will st
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is thus the inverse of the spatial frequency. Wavelength is determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. Wavelength is designated by the Greek letter lambda; the term wavelength is sometimes applied to modulated waves, to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids. Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, lower frequencies have longer wavelengths. Wavelength depends on the medium. Examples of wave-like phenomena are sound waves, water waves and periodic electrical signals in a conductor.
A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary. Water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary. Wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in sinusoidal waves over deep water a particle near the water's surface moves in a circle of the same diameter as the wave height, unrelated to wavelength; the range of wavelengths or frequencies for wave phenomena is called a spectrum. The name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any wave pattern can be described in terms of the independent propagation of sinusoidal components; the wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, where v is called the phase speed of the wave and f is the wave's frequency.
In a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the phase speed is the speed of light, about 3×108 m/s, thus the wavelength of a 100 MHz electromagnetic wave is about: 3×108 m/s divided by 108 Hz = 3 metres. The wavelength of visible light ranges from deep red 700 nm, to violet 400 nm. For sound waves in air, the speed of sound is 343 m/s; the wavelengths of sound frequencies audible to the human ear are thus between 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light. A standing wave is an undulatory motion. A sinusoidal standing wave includes stationary points of no motion, called nodes, the wavelength is twice the distance between nodes; the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed.
For example, for an electromagnetic wave, if the box has ideal metal walls, the condition for nodes at the walls results because the metal walls cannot support a tangential electric field, forcing the wave to have zero amplitude at the wall. The stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Wavelength and wave velocity are related just as for a traveling wave. For example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. Traveling sinusoidal waves are represented mathematically in terms of their velocity v, frequency f and wavelength λ as: y = A cos = A cos where y is the value of the wave at any position x and time t, A is the amplitude of the wave, they are commonly expressed in terms of wavenumber k and angular frequency ω as: y = A cos = A cos in which wavelength and wavenumber are related to velocity and frequency as: k = 2 π λ = 2 π f v = ω
An overhead projector is a variant of slide projector, used to display images to an audience.. An overhead projector works on the same principle as a 35mm slide projector, in which a focusing lens projects light from an illuminated slide onto a projection screen where a real image is formed; however some differences are necessitated by the much larger size of the transparencies used, the requirement that the transparency be placed face up. For the latter purpose, the projector includes a mirror just before or after the focusing lens to fold the optical system toward the horizontal; that mirror accomplishes a reversal of the image in order that the image projected onto the screen corresponds to that of the slide as seen by the presenter looking down at it, rather than a mirror image thereof. Therefore, the transparency is placed face up, in contrast with a 35mm slide projector or film projector where the slide's image is non-reversed on the side opposite the focusing lens; the device has sometimes been called a "Belshazzar", after Belshazzar's feast.
Because the focusing lens is much smaller than the transparency, a crucial role is played by the optical condenser which illuminates the transparency. Since this requires a large optical lens but may be of poor optical quality, a Fresnel lens is employed; the Fresnel lens is located at the glass plate on which the transparency is placed, serves to redirect most of the light hitting it into a converging cone toward the focusing lens. Without such a condenser at that point, most of the light would miss the focusing lens. Additionally, mirrors or other condensing elements below the Fresnel lens serve to increase the portion of the light bulb's output which reaches the Fresnel lens in the first place. In order to provide sufficient light on the screen, a high intensity bulb is used which must be fan cooled. Overhead projectors include a manual focusing mechanism which raises and lowers the position of the focusing lens in order to adjust the object distance to focus at the chosen image distance given the fixed focal length of the focusing lens.
This permits a range of projection distances. Increasing the projection distance increases the focusing system's magnification in order to fit the projection screen in use. Increasing the projection distance means that the same amount of light is spread over a larger screen, resulting in a dimmer image. With a change in the projection distance, the focusing must be readjusted for a sharp image. However, the condensing optics is optimized for one particular vertical position of the lens, corresponding to one projection distance. Therefore, when it is focused for a different projection distance, part of the light cone projected by the Fresnel lens towards the focusing lens misses that lens; this has the greatest effect towards the outer edges of the projected image, so that one sees either blue or brown fringing at the edge of the screen when the focus is towards an extreme. Using the projector near its recommended projection distance allows a focusing position where this is avoided and the intensity across the screen is uniform.
The lamp technology of an overhead projector is very simple compared to a modern LCD or DLP video projector. Most overheads use an high-power halogen lamp that may consume up to 750 watts. A high-flow blower is required to keep the bulb from melting due to the heat generated, this blower is on a timer that keeps it running for a period after the light is extinguished. Further, the intense heat accelerates failure of the high intensity lamp burning out in less than 100 hours, requiring replacement. In contrast, a modern LCD or DLP projector uses an arc lamp which has a higher luminous efficacy and lasts for thousands of hours. A drawback of that technology is the warm up time required for arc lamps. Older overhead projectors used a tubular quartz bulb, mounted above a bowl-shaped polished reflector. However, because the lamp was suspended above and outside the reflector, a large amount of light was cast to the sides inside the projector body, wasted, thus requiring a higher power lamp for sufficient screen illumination.
More modern overhead projectors use an integrated lamp and conical reflector assembly, allowing the lamp to be located deep within the reflector and sending a greater portion of its light towards the Fresnel lens. A useful innovation for overhead projectors with integrated lamps/reflectors is the quick-swap dual-lamp control, allowing two lamps to be installed in the projector in movable sockets. If one lamp fails during a presentation the presenter can move a lever to slide the spare into position and continue with the presentation, without needing to open the projection unit or waiting for the failed bulb to cool before replacing it; some ancient projectors like the magic lantern can be regarded as predecessors of the overhead projector. The steganographic mirror came closest to how the o
Michael Faraday FRS was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction and electrolysis. Although Faraday received little formal education, he was one of the most influential scientists in history, it was by his research on the magnetic field around a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics. Faraday established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena, he discovered the principles of electromagnetic induction and diamagnetism, the laws of electrolysis. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, it was due to his efforts that electricity became practical for use in technology; as a chemist, Faraday discovered benzene, investigated the clathrate hydrate of chlorine, invented an early form of the Bunsen burner and the system of oxidation numbers, popularised terminology such as "anode", "cathode", "electrode" and "ion".
Faraday became the first and foremost Fullerian Professor of Chemistry at the Royal Institution, a lifetime position. Faraday was an excellent experimentalist who conveyed his ideas in simple language. James Clerk Maxwell took the work of Faraday and others and summarized it in a set of equations, accepted as the basis of all modern theories of electromagnetic phenomena. On Faraday's uses of lines of force, Maxwell wrote that they show Faraday "to have been in reality a mathematician of a high order – one from whom the mathematicians of the future may derive valuable and fertile methods." The SI unit of capacitance is named in his honour: the farad. Albert Einstein kept a picture of Faraday on his study wall, alongside pictures of Isaac Newton and James Clerk Maxwell. Physicist Ernest Rutherford stated, "When we consider the magnitude and extent of his discoveries and their influence on the progress of science and of industry, there is no honour too great to pay to the memory of Faraday, one of the greatest scientific discoverers of all time."
Michael Faraday was born on 22 September 1791 in Newington Butts, now part of the London Borough of Southwark but was a suburban part of Surrey. His family was not well off, his father, was a member of the Glassite sect of Christianity. James Faraday moved his wife and two children to London during the winter of 1790 from Outhgill in Westmorland, where he had been an apprentice to the village blacksmith. Michael was born in the autumn of that year; the young Michael Faraday, the third of four children, having only the most basic school education, had to educate himself. At the age of 14 he became an apprentice to George Riebau, a local bookbinder and bookseller in Blandford Street. During his seven-year apprenticeship Faraday read many books, including Isaac Watts's The Improvement of the Mind, he enthusiastically implemented the principles and suggestions contained therein, he developed an interest in science in electricity. Faraday was inspired by the book Conversations on Chemistry by Jane Marcet.
In 1812, at the age of 20 and at the end of his apprenticeship, Faraday attended lectures by the eminent English chemist Humphry Davy of the Royal Institution and the Royal Society, John Tatum, founder of the City Philosophical Society. Many of the tickets for these lectures were given to Faraday by William Dance, one of the founders of the Royal Philharmonic Society. Faraday subsequently sent Davy a 300-page book based on notes that he had taken during these lectures. Davy's reply was immediate and favourable. In 1813, when Davy damaged his eyesight in an accident with nitrogen trichloride, he decided to employ Faraday as an assistant. Coincidentally one of the Royal Institution's assistants, John Payne, was sacked and Sir Humphry Davy had been asked to find a replacement. Soon Davy entrusted Faraday with the preparation of nitrogen trichloride samples, they both were injured in an explosion of this sensitive substance. In the class-based English society of the time, Faraday was not considered a gentleman.
When Davy set out on a long tour of the continent in 1813–15, his valet did not wish to go, so instead, Faraday went as Davy's scientific assistant and was asked to act as Davy's valet until a replacement could be found in Paris. Faraday was forced to fill the role of valet as well as assistant throughout the trip. Davy's wife, Jane Apreece, refused to treat Faraday as an equal, made Faraday so miserable that he contemplated returning to England alone and giving up science altogether; the trip did, give him access to the scientific elite of Europe and exposed him to a host of stimulating ideas. Faraday married Sarah Barnard on 12 June 1821, they met through their families at the Sandemanian church, he confessed his faith to the Sandemanian congregation the month after they were married. They had no children. Faraday was a devout Christian. Well after his marriage, he served as deacon and for two terms as an elder in the meeting house of his youth, his church was located at Paul's Alley in the Barbican.
This meeting house relocated in 1862 to Islington.