Luminism is an American landscape painting style of the late 19th century characterized by effects of light in landscapes through the use of aerial perspective and concealing visible brushstrokes. Luminist landscapes emphasize tranquility and often depict calm, reflective water and a soft, hazy sky.

The term luminism was introduced by 20th century art historians to describe a painting style that developed as an offshoot of the Hudson River school. The artists who painted in this style did not refer to their own work as luminism, nor did they articulate any common painting philosophy outside of the guiding principles of the Hudson River school.

Luminism shares an emphasis on the effects of light with impressionism. However, the two styles are markedly different. Luminism is characterized by attention to detail and the hiding of brushstrokes, while impressionism is characterized by lack of detail and an emphasis on brushstrokes. Luminism preceded impressionism, and the artists who painted in a luminist style were in no way influenced by impressionism.

A triskelion is a symbol consisting of three interlocked spirals or or any similar symbol with three protrusions and a threefold rotational symmetry. It appears in many early cultures as a heraldic emblem on shields depicted on Greek pottery. The triple spiral motif is a Neolithic symbol in Western Europe. It is carved into the rock of a stone lozenge near the main entrance of the prehistoric Newgrange monument in County Meath, Ireland.

The triskelion is used by some polytheistic reconstructionist and neopagan groups. As a Celtic symbol, it is found primarily amongst groups with a Celtic cultural orientation and, less frequently, can also be found in use by some Germanic neopagan groups and eclectic or syncretic traditions such as Wicca.

In the north of Spain, the triskelion is used as a symbol of Galizan and Asturian nationalists. The triskele was used by Galician nationalists as early as 1930, although its use as a contemporary fashion icon only started during the Celtic revival of the 1970s. Currently, the Department of Agriculture of the devolved government of Galicia uses a triskele as its corporate logo.

A triskelion pattern forms part of the United States Department of Transportation seal. The three comma shapes represent air, land, and sea transportation. The seal was adopted on February 1, 1967. A triskelion is the basis for the roundel of the Irish Air Corps. It is loosely based on the Flag of Ireland and traditional Celtic designs. 

A triskelion shape was used in the design of a common plastic adapter for vinyl records, which allowed larger center holed 45 rpm records to spin on players designed for smaller center-holed 33 1/3 rpm records.

Summum bonum is an expression used in medieval philosophy to describe the ultimate importance, the singular and most ultimate end which human beings are to pursue. The summum bonum is generally thought of as being an end in itself, and at the same time containing all other good. In Hinduism and other Eastern Religions, Summum bonum is cognate with such concepts as Dharma, Tao, Shreyas, Moksha, Liberation, Jeevan Mukti, and Self Realization.

The concept, as well as the philosophical and theological consequences drawn from the purported existence of a more or less clearly defined summum bonum, could be traced back to the earliest forms of monotheism. In the Western world, the concept was introduced by the neoplatonic philosophers, and described as a feature of the Christian God by Saint Augustine in On the Nature of Good, written circa 399. Augustine denies the positive existence of absolute evil, describing a world with God as the supreme good at the center, and defining different grades of evil as different stages of remoteness from that center.

Experience soon teaches that all desires cannot be satisfied, that they are conflicting, and that some good must be foregone in order to secure another. Hence the necessity of weighing the relative value of good, of classifying it, and of ascertaining which good must be procured at the loss of another. The result is the division of good into two great classes, the physical and the moral, happiness and virtue. Within either class it is comparatively easy to determine the relation of particular good things to one another, but it has proven far more difficult to fix the relative excellence of the two classes of virtue and happiness. If happiness and virtue are mutually exclusive, we have to choose between the two, and this choice is a momentous one. But their incompatibility may be only on the surface. Indeed, the hope is ever recurring that the sovereign good includes both, and that there is some way of reconciling them.

A phosphene is an optic phenomenon characterized by the experience of seeing light without light actually entering the eye. Phosphenes can be directly induced by mechanical, electrical, or magnetic stimulation of the retina or visual cortex as well as by random firing of cells in the visual system. Phosphenes have been reported by meditators and people who go for long periods without visual stimulation (also known as the prisoner’s cinema).

The most common phosphenes are pressure phosphenes caused by rubbing the closed eyes. The pressure mechanically stimulates the cells of the retina. Experiences include a darkening of the visual field that moves against the rubbing, a diffuse colored patch that also moves against the rubbing, a scintillating and ever-changing and deforming light grid with occasional dark spots (like a crumpling fly-spotted flyscreen), and a sparse field of intense blue points of light.

Pressure phosphenes can persist briefly after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen on the visual scene. Herman Helmholtz and others have published drawings of their pressure phosphenes. One example of a pressure phosphene is demonstrated by gently pressing the side of your eye and observing a colored ring of light on the opposite side, as detailed by Isaac Newton.

Another common phosphene is “seeing stars,” from a sneeze, a heavy and deep cough, blowing of the nose, a blow on the head or low blood pressure (such as on standing up too quickly or prior to fainting). It is possible these involve some mechanical stimulation of the retina, but they may also involve mechanical and metabolic stimulation of neurons of the visual cortex or of other parts of the visual system.

Phosphenes have also been created by intense, changing magnetic fields, such as with transcranial magnetic stimulation. These fields can be positioned on different parts of the head to stimulate cells in different parts of the visual system. They also can be induced by alternating currents that entrain neural oscillation as with trancranial alternating-current stimulation. In this case they appear in the peripheral visual field. Astronauts exposed to radiation in space report seeing phosphenes.

Cave paintings are paintings on cave walls and ceilings, and the term is used especially for those dating to prehistoric times. The earliest known European cave paintings date to Aurignacian, some 32,000 years ago. The purpose of the paleolithic cave paintings is not known. The evidence suggests that they were not merely decorations of living areas, since the caves in which they have been found do not have signs of ongoing habitation. Also, they are often in areas of caves that are not easily accessed. Some theories hold that they may have been a way of communicating with others, while other theories ascribe them a religious or ceremonial purpose.

The most common themes in cave paintings are large wild animals, such as bison, horses, aurochs, and deer, and tracings of human hands as well as abstract patterns, called finger flutings. Drawings of humans were rare and are usually schematic rather than the more naturalistic animal subjects. One explanation for this is that realistically painting the human form was forbidden by a powerful religious taboo. Many of the paintings were drawn with red and yellow ochre, hematite, manganese oxide and charcoal. Sometimes the silhouette of the animal was incised in the rock first.

Henri Breuil interpreted the paintings as being hunting magic, meant to increase the number of animals. As there are some clay sculptures that seem to have been the targets of spears, this may partly be true, but does not explain the pictures of predators such as the lion or the bear.

An alternative theory based on ethnographic studies of contemporary hunter-gatherer societies, is that the paintings were made by Cro-Magnon shamans. The shaman would retreat into the darkness of the caves, enter into a trance state and then paint images of their visions, perhaps with some notion of drawing power out of the cave walls themselves. This goes some way toward explaining the remoteness of some of the paintings, which often occur in deep or small caves, and the variety of subject matter, from prey animals to predators and human hand-prints.

The Summerland is the name given by Wiccans and other earth-based religions for their conceptualization of an afterlife. The common portrayal of the Summerland is as a place of rest for souls in between their earthly incarnations. Some believe that after one experiences life to its fullest, and has come to know and understand every aspect and emotion of physical human life, usually after many reincarnations, their deity will allow them to stay in the Summerland for an eternal afterlife.

Another common element is that the soul has little, if any, recollection of the Summerland once it arrives on the mortal plane again. The Summerland is also envisioned as a place for recollection and reunion with deceased loved ones.

As the name suggests, it is often envisaged as a place of beauty and peace, where everything people hold close to their hearts is preserved in its fullest beauty for eternity. It is envisioned as containing wide fields of rolling green hills and lush grass. In many ways, this ideology is similar to the Welsh view of Annwn as an afterlife realm. However, the Summerland was also viewed in traditions of Spiritualism, where Wicca got the term itself.

The essence of the Summerland is that it is a resting ground where souls can reflect on the life they led, see if they learned the lesson they had intended on learning, and then try again in due course. The Summerland is not seen as a place of judgement, but rather, as a spiritual self-evaluation where a soul is able to review its life and gain an understanding of the total impact its actions had on the world. Some may believe each particular lesson and life is chosen and planned out by the soul itself while in Summerland, whereas others may believe that lessons are planned by an external party such as deities or spirit guides.

Usonia is a word used by American architect Frank Lloyd Wright to refer to his vision for the landscape of the United States, including the planning of cities and the architecture of buildings. Wright proposed the use of the adjective Usonian in place of American to describe the particular New World character of the American landscape as distinct and free of previous architectural conventions.

Usonian is a term usually referring to a group of approximately fifty middle-income family homes designed by Frank Lloyd Wright beginning in 1936 with the Jacobs House. The Usonian Homes were typically small, single-story dwellings without a garage or much storage, L-shaped to fit around a garden terrace on odd (and cheap) lots.

They were environmentally conscious with native materials, flat roofs and large cantilevered overhangs for passive solar heating and natural cooling, natural lighting with clerestory windows, and radiant-floor heating. A strong visual connection between the interior and exterior spaces is an important characteristic of all Usonian homes.

Variants of the Jacobs House design are still in existence today and do not look overly dated. The Usonian design is considered among the aesthetic origins of the popular ranch tract home popular in the American west of the 1950s.

Multistable perceptual phenomena are a rare form of visual perception phenomena which is characterized by an unpredictable sequence of spontaneous subjective changes.

Perceptual multistability can be evoked by visual patterns that are too ambiguous for the human visual system to recognise with one unique interpretation. Famous examples include the Necker cube, structure from motion, monocular rivalry and binocular rivalry, but many more visually ambiguous patterns are known. Since most of these images lead to an alternation between two mutually exclusive perceptual states, they are sometimes also referred to as bistable perception.

Transitions from one percept to its alternative are called perceptual reversals. They are spontaneous and stochastic events which cannot be eliminated by intentional efforts, although some control over the alternation process is learnable. Reversal rates vary drastically between stimuli and observers, and has been found to be slower for people with Bipolar disorder due to “sticky” interhemispheric switch in bipolar disorder. 

Human interest in these phenomena can be traced back to antiquity. The fascination of multistable perception probably comes from the active nature of endogenous perceptual changes or from the dissociation of dynamic perception from constant sensory stimulation. Multistable perception was a common feature in the artwork of the Dutch lithographer M. C. Escher, who was strongly influenced by mathematical physicists such as Roger Penrose. 

Photographs of craters, from either the moon or other planets including our own, can exhibit this phenomenon. Craters, in stereo imaging, such as our eyes, should appear to be pit-like structures. However in mono-vision, such as that of photographs, the elimination of our depth perception causes multistable perception to take over, and this can cause the craters to inverse their depth values and instead look like plateaus rather than pits. Sometimes rotating the image so that the photographic direction of the source of light matches a light source in the room can cause the correct perception to suddenly switch.