Canada balsam
Canada balsam called Canada turpentine or balsam of fir, is a turpentine made from the resin of the balsam fir tree of boreal North America. The resin, dissolved in essential oils, is a viscous, colourless or yellowish liquid that turns to a transparent yellowish mass when the essential oils have been allowed to evaporate. Canada balsam is amorphous. Since it does not crystallize with age, its optical properties do not deteriorate. However, it has poor solvent resistance. Due to its high optical quality and the similarity of its refractive index to that of crown glass and filtered Canada balsam was traditionally used in optics as an invisible-when-dry glue for glass, such as lens elements. Lenses glued with Canada balsam are called cemented lenses. Other optical elements can be cemented with Canada balsam, such as two prisms bonded to form a beam splitter. Balsam was phased out as an optical adhesive during World War II, in favour of polyester and urethane-based adhesives. In modern optical manufacturing, UV-cured epoxies are used to bond lens elements.
Canada balsam was commonly used for making permanent microscope slides. From about 1830 molten Canada balsam was used for microscope slides Canada balsam in solution was introduced in 1843, becoming popular in the 1850s. In biology, for example, it can be used to conserve microscopic samples by sandwiching the sample between a microscope slide and a glass coverslip, using Canada balsam to glue the arrangement together and enclose the sample to conserve it. Xylene balsam, Canada balsam dissolved in xylene, is used for preparing slide mounts; some workers prefer terpene resin for slide mounts, as it is both less acidic and cheaper than balsam. Synthetic resins have replaced organic balsams for such applications. Another important application of Canada balsam is in the construction of the Nicol prism. A Nicol prism consists of a calcite crystal cut into two halves. Canada balsam is placed between the two layers. Calcite is an anisotropic crystal and has different refractive indices for rays polarized along directions parallel and perpendicular to its optic axis.
These rays with differing refractive indices are known as the extraordinary rays. The refractive index for Canada balsam is in between the refractive index for the ordinary and extraordinary rays. Hence the ordinary ray will be internally reflected; the emergent ray will be linearly polarized, traditionally this has been one of the popular ways of producing polarized light. Some other uses include: in geology, it is used as a common thin section cement and glue and for refractive-index studies and tests, such as the Becke line test. Balm of Gilead, a healing compound made from the resinous gum of Commiphora gileadensis
Ceramic
A ceramic is a solid material comprising an inorganic compound of metal, non-metal or metalloid atoms held in ionic and covalent bonds. Common examples are earthenware and brick; the crystallinity of ceramic materials ranges from oriented to semi-crystalline and completely amorphous. Most fired ceramics are either vitrified or semi-vitrified as is the case with earthenware and porcelain. Varying crystallinity and electron composition in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators. With such a large range of possible options for the composition/structure of a ceramic, the breadth of the subject is vast, identifiable attributes are difficult to specify for the group as a whole. General properties such as high melting temperature, high hardness, poor conductivity, high moduli of elasticity, chemical resistance and low ductility are the norm, with known exceptions to each of these rules. Many composites, such as fiberglass and carbon fiber, while containing ceramic materials, are not considered to be part of the ceramic family.
The earliest ceramics made by humans were pottery objects or figurines made from clay, either by itself or mixed with other materials like silica and sintered in fire. Ceramics were glazed and fired to create smooth, colored surfaces, decreasing porosity through the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates. Ceramics now include domestic and building products, as well as a wide range of ceramic art. In the 20th century, new ceramic materials were developed for use in advanced ceramic engineering, such as in semiconductors; the word "ceramic" comes from the Greek word κεραμικός, "of pottery" or "for pottery", from κέραμος, "potter's clay, pottery". The earliest known mention of the root "ceram-" is the Mycenaean Greek ke-ra-me-we, "workers of ceramics", written in Linear B syllabic script; the word "ceramic" may be used as an adjective to describe a material, product or process, or it may be used as a noun, either singular, or, more as the plural noun "ceramics".
A ceramic material is an inorganic, non-metallic crystalline oxide, nitride or carbide material. Some elements, such as carbon or silicon, may be considered ceramics. Ceramic materials are brittle, strong in compression, weak in shearing and tension, they withstand chemical erosion that occurs in other materials subjected to acidic or caustic environments. Ceramics can withstand high temperatures, ranging from 1,000 °C to 1,600 °C. Glass is not considered a ceramic because of its amorphous character. However, glassmaking involves several steps of the ceramic process, its mechanical properties are similar to ceramic materials. Traditional ceramic raw materials include clay minerals such as kaolinite, whereas more recent materials include aluminium oxide, more known as alumina; the modern ceramic materials, which are classified as advanced ceramics, include silicon carbide and tungsten carbide. Both are valued for their abrasion resistance and hence find use in applications such as the wear plates of crushing equipment in mining operations.
Advanced ceramics are used in the medicine, electronics industries and body armor. Crystalline ceramic materials are not amenable to a great range of processing. Methods for dealing with them tend to fall into one of two categories – either make the ceramic in the desired shape, by reaction in situ, or by "forming" powders into the desired shape, sintering to form a solid body. Ceramic forming techniques include shaping by hand, slip casting, tape casting, injection molding, dry pressing, other variations. Noncrystalline ceramics, being glass, tend to be formed from melts; the glass is shaped when either molten, by casting, or when in a state of toffee-like viscosity, by methods such as blowing into a mold. If heat treatments cause this glass to become crystalline, the resulting material is known as a glass-ceramic used as cook-tops and as a glass composite material for nuclear waste disposal; the physical properties of any ceramic substance are a direct result of its crystalline structure and chemical composition.
Solid-state chemistry reveals the fundamental connection between microstructure and properties such as localized density variations, grain size distribution, type of porosity and second-phase content, which can all be correlated with ceramic properties such as mechanical strength σ by the Hall-Petch equation, toughness, dielectric constant, the optical properties exhibited by transparent materials. Ceramography is the art and science of preparation and evaluation of ceramic microstructures. Evaluation and characterization of ceramic microstructures is implemented on similar spatial scales to that used in the emerging field of nanotechnology: from tens of angstroms to tens of micrometers; this is somewhere between the minimum wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, micro-
Rock microstructure
Rock microstructure includes the texture of a rock and the small scale rock structures. The words "texture" and "microstructure" are interchangeable, with the latter preferred in modern geological literature. However, texture is still acceptable because it is a useful means of identifying the origin of rocks, how they formed, their appearance. Textures are penetrative fabrics of rocks; this is similar in many ways to foliations, except a texture does not carry structural information in terms of deformation events and orientation information. Structures occur above. Microstructure analysis describes the textural features of the rock, can provide information on the conditions of formation and subsequent deformation, folding or alteration events. Description of sedimentary rock microstructure aims to provide information on the conditions of deposition of the sediment, the paleo-environment, the provenance of the sedimentary material. Methods involve description of clast size, composition, rounding or angularity and description of the matrix.
Sedimentary microstructures may include microscopic analogs of larger sedimentary structural features such as cross-bedding, syn-sedimentary faults, sediment slumping, cross-stratification, etc. The maturity of a sediment is related not only to the sorting, but to the fragment sphericity and composition. Quartz-only sands are more mature than greywacke. Fragment shape gives information on the length of sediment transport; the more rounded the clasts, the more water-worn they are. Particle shape includes rounding. Form indicates whether a grain is more platy. Roundness refers to the degree of sharpness of the edges of a grain; the surface texture of grains frosted, or marked by small pits and scratches. This information can be seen best under a binocular microscope, not in a thin section. Composition of the clasts can give clues as to the derivation of a rock's sediments. For instance, volcanic fragments, fragments of cherts, well-rounded sands all imply different sources; the matrix of a sedimentary rock and the mineral cement holding it together are all diagnostic.
Diagenesis results in a weak bedding-plane foliation. Other effects can include flattening of pressure dissolution and sub-grain deformation. Mineralogical changes may include zeolite or other authigenic minerals forming in low-grade metamorphic conditions. Sorting is used to describe the uniformity of grain sizes within a sedimentary rock. Understanding sorting is critical to making inferences on the degree of maturity and length of transport of a sediment. Sediments become sorted on the basis of density, because of the energy of the transporting medium. High energy currents can carry larger fragments; as the energy decreases, heavier particles are deposited and lighter fragments continue to be transported. This results in sorting due to density. Sorting can be expressed mathematically by the standard deviation of the grain-size frequency curve of a sediment sample, expressed as values of φ. Values range from <0.35φ to >4.00φ. The study of metamorphic rock microstructures aims to determine the timing and conditions of deformations, mineral growth and overprinting of subsequent deformation events.
Metamorphic microstructures include textures formed by the development of foliation and overprinting of foliations causing crenulations. The relationship of porphyroblasts to the foliations and to other porphyroblasts can provide information on the order of formation of metamorphic assemblages or facies of minerals. Shear textures are suited to analysis by microstructural investigations in mylonites and other disturbed and deformed rocks. On the thin section and hand specimen scale a metamorphic rock may manifest a planar penetrative fabric called a foliation or a cleavage. Several foliations may be present in a rock. Identifying a foliation and its orientation is the first step in analysis of foliated metamorphic rocks. Gaining information on when the foliation formed is essential to reconstructing a P-T-t path for a rock, as the relationship of a foliation to porphyroblasts is diagnostic of when the foliation formed, the P-T conditions which existed at that time. Linear structures in a rock may arise from the intersection of two foliations or planar structures, such as a sedimentary bedding plane and a tectonically induced cleavage plane.
The degree of lineation compared with the degree of foliation for certain strain markers in deformed rocks are plotted on a Flinn diagram. Distinctive textures form as a consequence of ductile shear; the microstructures of ductile shear zones are C-planes and C' planes. S-planes or schistosity planes are parallel with the shear direction and are defined by micas or platy minerals. Define the flattened long-axis of the strain ellipse. C-planes or cissalement planes form oblique to the shear plane; the angle between the C and S planes is always acute, defines the shear sense. The lower the C-S angle the greater the strain; the C' planes are observed except in ultradeformed mylonites, form nearly perpendicular to the S-plane. Other microstructures which can give sense of shear include sigmoidal veins mica fish rotated porphyroblasts Analysis of igneous rock microstructure may complement descriptions on the hand specimen and outcrop
Mineral
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
Climatic geomorphology
Climatic geomorphology is the study of the role of climate in shaping landforms and the earth-surface processes. An approach used in climatic geomorphology is to study relict landforms to infer ancient climates. Being concerned about past climates climatic geomorphology considered sometimes to be an aspect of historical geology. Since landscape features in one region might have evolved under climates different than today, studying climatically disparate regions might help understand present-day landscapes. For example, Julius Büdel studied both cold-climate processes in Svalbard and weathering processes in tropical India to understand the origin of the relief of Central Europe, which he argued was a palimpsest of landforms formed at different times and under different climates; the various subbranches of climatic geomorhpology focus on specific climatic environments. Desert geomorphology or the geomorphology of arid and semi-arid lands shares many landsforms and processes with more humid regions.
One distinctive feature is the sparse or lacking vegetation cover, which influences fluvial and slope processes, related to wind and salt activity. Early work on desert geomorphology was done by Western explorers of the colonies of their respective countries in Africa, in frontier regions of their own countries or in the deserts of foreign countries such as the Ottoman Empire, the Russian Empire and China. Since the 1970s desert geomorphology in Earth has served to find analogues to Martian landscapes; as a discipline periglacial geomorphology is close but different to Quaternary science and geocryology. Periglacial geomorphology is concerned with non-glacial cold-climate landforms in areas with and without permafrost. Albeit the definition of what a periglacial zone is not clear-cut a conservative estimate is that a quarter of Earth's land surface has periglacial conditions. Beyond this quarter an additional quarter or fifth or Earth's land surface had periglacial conditions at some time during the Pleistocene.
In periglacial geomorphology noted researchers include Johan Gunnar Andersson, Walery Łoziński, Anders Rapp and Jean Tricart. If the tropics is defined as the area between 35° N and 35° S about 60% of Earth's surface lies within this zone. During most of the 20th century tropical geomorphology was neglected due to a bias towards temperate climates, when dealt with it was highlighted as "exotic". Tropical geomorphology do differ from other areas in the intensities and rates at which surface processes operate, not by the type of processes; the tropics are characterized by particular climates, that may be humid. Relative to temperate zones the tropics contain areas of high temperatures, high rainfall intensities and high evapotranspiration all of which are climatic features relevant for surface processes. Another characteristic, not related to present-day climate per see, is that a large portion of the tropics have a low relief, inherited from the continent of Gondwana. Julius Büdel, Pierre Birot and Jean Tricart have suggested that tropical rivers are dominated by fine-grained suspended load derived from advanced chemical weathering, this would make them less erosive than rivers elsewhere.
Some landforms thought as tropical like bornhardts are more related to lithology and rock structure than climate. Climatic geomorphologists have devised various schemes that divide Earth's surface into various morphoclimatic zones. However, only some processes and landforms can be associated with particular climates, meaning that they are zonal. Despite this, azonal processes and landforms might still take on particular characteristics when developing under the influence of particular climates; when identified, morphoclimatic zones do lack sharp boundaries and tend to grade from one type to another resulting in that only the core of the zone has all expected attributes. Influential morphoclimatic zoning schemes are those of Julius Büdel and of Jean Tricart and André Cailleux. Büdel's schemes stresses planation and valley-cutting in relation to climate, arguing the valley-cutting is dominant in subpolar regions while planation is so in the tropics; as such this scheme is concerned not only with processes but with end-products of geomorphic activity.
The scheme of Tricart and Cailleux emphasizes the relationship between geomorphology and vegetation. An early attempt at morphoclimatic zoning is that of Albrecht Penck in 1910, who divided Earth in three zones depending on the evaporation-precipitation ratios. A 1994 review argues that only the concepts of desert, periglacial and a few coastal morphoclimatic zones are justified; these zones amounts to about half of Earth's land surface, the remaining half cannot be explained in simple terms by climate-landform interactions. The limitations of morphoclimatic zoning were discussed by Siegfried Passarge in 1926 who considered vegetation and the extent of weathered material as having more direct impact than climate in many parts of the World. According to M. A. Summerfield large-scale zoning of the relief of Earth's surface is better explained on the basis of plate tectonics than on climate. An example of this are the Scandinavian Mountains whose plateau areas and valleys relate to the history of uplift and not to climate.
Piotr Migoń has questioned the validity of certain morphoclimatic zonation schemes since they are named after processes, like planation, that might not occurring at all in large swathes of the zone. Referring to the 1977 scheme of Büdel Migoń states: Is i
Polarizer
A polarizer or polariser is an optical filter that lets light waves of a specific polarization pass through while blocking light waves of other polarizations. It can filter a beam of light of undefined or mixed polarization into a beam of well-defined polarization, polarized light; the common types of polarizers are circular polarizers. Polarizers are used in many optical techniques and instruments, polarizing filters find applications in photography and LCD technology. Polarizers can be made for other types of electromagnetic waves besides light, such as radio waves, X-rays. Linear polarizers can be divided into two general categories: absorptive polarizers, where the unwanted polarization states are absorbed by the device, beam-splitting polarizers, where the unpolarized beam is split into two beams with opposite polarization states. Polarizers which maintain the same axes of polarization with varying angles of incidence are called Cartesian polarizers, since the polarization vectors can be described with simple Cartesian coordinates independent from the orientation of the polarizer surface.
When the two polarization states are relative to the direction of a surface, they are termed s and p. This distinction between Cartesian and s–p polarization can be negligible in many cases, but it becomes significant for achieving high contrast and with wide angular spreads of the incident light. Certain crystals, due to the effects described by crystal optics, show dichroism, preferential absorption of light, polarized in particular directions, they can therefore be used as linear polarizers. The best known crystal of this type is tourmaline. However, this crystal is used as a polarizer, since the dichroic effect is wavelength dependent and the crystal appears coloured. Herapathite is dichroic, is not coloured, but is difficult to grow in large crystals. A Polaroid polarizing filter functions on an atomic scale to the wire-grid polarizer, it was made of microscopic herapathite crystals. Its current H-sheet form is made from polyvinyl alcohol plastic with an iodine doping. Stretching of the sheet during manufacture causes the PVA chains to align in one particular direction.
Valence electrons from the iodine dopant are able to move linearly along the polymer chains, but not transverse to them. So incident light polarized; the durability and practicality of Polaroid makes it the most common type of polarizer in use, for example for sunglasses, photographic filters, liquid crystal displays. It is much cheaper than other types of polarizer. A modern type of absorptive polarizer is made of elongated silver nano-particles embedded in thin glass plates; these polarizers are more durable, can polarize light much better than plastic Polaroid film, achieving polarization ratios as high as 100,000:1 and absorption of polarized light as low as 1.5%. Such glass polarizers perform best for short-wavelength infrared light, are used in optical fiber communications. Beam-splitting polarizers split the incident beam into two beams of differing linear polarization. For an ideal polarizing beamsplitter these would be polarized, with orthogonal polarizations. For many common beam-splitting polarizers, only one of the two output beams is polarized.
The other contains a mixture of polarization states. Unlike absorptive polarizers, beam splitting polarizers do not need to absorb and dissipate the energy of the rejected polarization state, so they are more suitable for use with high intensity beams such as laser light. True polarizing beamsplitters are useful where the two polarization components are to be analyzed or used simultaneously; when light reflects at an angle from an interface between two transparent materials, the reflectivity is different for light polarized in the plane of incidence and light polarized perpendicular to it. Light polarized in the plane is said to be p-polarized, while that polarized perpendicular to it is s-polarized. At a special angle known as Brewster's angle, no p-polarized light is reflected from the surface, thus all reflected light must be s-polarized, with an electric field perpendicular to the plane of incidence. A simple linear polarizer can be made by tilting a stack of glass plates at Brewster's angle to the beam.
Some of the s-polarized light is reflected from each surface of each plate. For a stack of plates, each reflection depletes the incident beam of s-polarized light, leaving a greater fraction of p-polarized light in the transmitted beam at each stage. For visible light in air and typical glass, Brewster's angle is about 57°, about 16% of the s-polarized light present in the beam is reflected for each air-to-glass or glass-to-air transition, it takes many plates to achieve mediocre polarization of the transmitted beam with this approach. For a stack of 10 plates, about 3% of the s-polarized light is transmitted; the reflected beam, while polarized, is spread out and may not be useful. A more useful polarized beam can be obtained by tilting the pile of plates at a steeper angle to the incident beam. Counterintuitively, using incident angles greater than Brewster's angle yields a higher degree of polarization of the transmitted beam, at the expense of decreased overall transmission. For angles of incidence steeper than 80° the polarization of the transmitted beam can approach 100% with as few as four plates, although the transmitted intensity is low in this case.
Adding more plates and reducing
Archaeology
Archaeology, or archeology, is the study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, biofacts or ecofacts and cultural landscapes. Archaeology can be considered a branch of the humanities. In North America archaeology is a sub-field of anthropology, while in Europe it is viewed as either a discipline in its own right or a sub-field of other disciplines. Archaeologists study human prehistory and history, from the development of the first stone tools at Lomekwi in East Africa 3.3 million years ago up until recent decades. Archaeology is distinct from palaeontology, the study of fossil remains, it is important for learning about prehistoric societies, for whom there may be no written records to study. Prehistory includes over 99% of the human past, from the Paleolithic until the advent of literacy in societies across the world. Archaeology has various goals, which range from understanding culture history to reconstructing past lifeways to documenting and explaining changes in human societies through time.
The discipline involves surveying and analysis of data collected to learn more about the past. In broad scope, archaeology relies on cross-disciplinary research, it draws upon anthropology, art history, ethnology, geology, literary history, semiology, textual criticism, information sciences, statistics, paleography, paleontology and paleobotany. Archaeology developed out of antiquarianism in Europe during the 19th century, has since become a discipline practiced across the world. Archaeology has been used by nation-states to create particular visions of the past. Since its early development, various specific sub-disciplines of archaeology have developed, including maritime archaeology, feminist archaeology and archaeoastronomy, numerous different scientific techniques have been developed to aid archaeological investigation. Nonetheless, archaeologists face many problems, such as dealing with pseudoarchaeology, the looting of artifacts, a lack of public interest, opposition to the excavation of human remains.
The science of archaeology grew out of the older multi-disciplinary study known as antiquarianism. Antiquarians studied history with particular attention to ancient artifacts and manuscripts, as well as historical sites. Antiquarianism focused on the empirical evidence that existed for the understanding of the past, encapsulated in the motto of the 18th-century antiquary, Sir Richard Colt Hoare, "We speak from facts not theory". Tentative steps towards the systematization of archaeology as a science took place during the Enlightenment era in Europe in the 17th and 18th centuries. In Europe, philosophical interest in the remains of Greco-Roman civilization and the rediscovery of classical culture began in the late Middle Age. Flavio Biondo, an Italian Renaissance humanist historian, created a systematic guide to the ruins and topography of ancient Rome in the early 15th century, for which he has been called an early founder of archaeology. Antiquarians of the 16th century, including John Leland and William Camden, conducted surveys of the English countryside, drawing and interpreting the monuments that they encountered.
One of the first sites to undergo archaeological excavation was Stonehenge and other megalithic monuments in England. John Aubrey was a pioneer archaeologist who recorded numerous megalithic and other field monuments in southern England, he was ahead of his time in the analysis of his findings. He attempted to chart the chronological stylistic evolution of handwriting, medieval architecture and shield-shapes. Excavations were carried out by the Spanish military engineer Roque Joaquín de Alcubierre in the ancient towns of Pompeii and Herculaneum, both of, covered by ash during the Eruption of Mount Vesuvius in AD 79; these excavations began in 1748 in Pompeii, while in Herculaneum they began in 1738. The discovery of entire towns, complete with utensils and human shapes, as well the unearthing of frescos, had a big impact throughout Europe. However, prior to the development of modern techniques, excavations tended to be haphazard; the father of archaeological excavation was William Cunnington. He undertook excavations in Wiltshire from around 1798.
Cunnington made meticulous recordings of Neolithic and Bronze Age barrows, the terms he used to categorize and describe them are still used by archaeologists today. One of the major achievements of 19th-century archaeology was the development of stratigraphy; the idea of overlapping strata tracing back to successive periods was borrowed from the new geological and paleontological work of scholars like William Smith, James Hutton and Charles Lyell. The application of stratigraphy to archaeology first took place with the excavations of prehistorical and Bronze Age sites. In the third and fourth decades of the 19th-century, archaeologists like Jacques Boucher de Perthes and Christian Jürgensen Thomsen began to put the artifacts they had found in chronological order. A major figure in the development of archaeology into a rigorous science was the army officer and ethnologist, Augustus Pitt Rivers, who began excavations on his land in England in the 1880s, his approach was methodical by the standards of the time, he is regarded as the first scientific archaeologist.
He arranged his artifacts by type or "typologically, within types by date or "chronologically"
One or more of the preceding sentences incorporates text from a publication now in the public domain: Flett, John Smith (1911). . In Chisholm, Hugh (ed.). Encyclopædia Britannica. 21 (11th ed.). Cambridge University Press. pp. 323–333.
One or more of the preceding sentences incorporates text from a publication now in the 
