Oculus

Oculus (pronounced ok-yuh-luhs)

(1) In anatomy, an eye.

(2) In architecture, a window or other circular (or oval) opening, especially one at the apex of a dome.

(3) In archaeology, a design representing an eye, as on funerary pottery found in megalithic tombs of Europe.

(4) In the mechanical engineering (associated with fluid dynamics), the central boss of a volute.

(5) In poetic and literary use, luminary of the sun and stars; eye of the soul, mind's eye; a spot resembling an eye, such as on a peacock feather; a principle ornament or the main feature of something.

(6) In botany, a bud, bulb or knob on many roots, on the reed etc.

(7) As oculist (plural oculists), one who practices the discipline of oculism (an archaic name for an ophthalmologist or optometrist).

1857: From the Latin oculus (an eye), from the Proto-Italic okwelos, from the primitive Indo-European hsokw (eye; to see).  It was cognate with the Sanskrit अक्षि (ákṣi), the Ancient Greek ὄσσε (ósse), the Gothic augō, the Old English ēaġe (from which Modern English would gain eye) & the Proto-Slavic oko.  Originating in antiquity, it was a widely used feature of Byzantine and Neoclassical architecture, known in French as the œil de boeuf (bull's-eye).  The noun plural is oculi.  An impressively long word with the same root is ocularpneumoplethysmography, a non-invasive technique for detecting carotid stenosis by measurement of ophthalmic artery pressure.  Oculus & oculist are nouns; the noun plural is oculi (under the standard rules of English plural formations, the result would be oculuses by that seems to have been too awful to contemplate). 

The Pantheon

The Pantheon in Rome (from the Latin Pantheum, from the Ancient Greek Πάνθειον (Pantheion) ([temple] of all the gods) was built as a Roman temple and since the 609 has been a Roman Catholic church (Basilica di Santa Maria ad Martyres or Basilica of Saint Mary and the Martyrs).  It was built on the site of an earlier temple constructed during the time of Christ and rebuilt by the Emperor Hadrian circa 126 AD, the actual date uncertain because Hadrian retained the old inscriptions.

Cylindrical with a portico of sixteen staggered Corinthian columns, the dome has a diameter of 43.2m (142 feet) and was for over 1300 years the largest in the world and remains, after some two-thousand years, the largest unreinforced concrete dome, a feat achieved by a gradual reduction in the thickness and weight of the materials used for the upper layers.  Each of the granite columns weigh sixty tons.  Quarried in Egypt, they were dragged 100 km (60 miles), placed on barges and shipped up the Nile to Alexandria where they were transferred to boats to cross the Mediterranean to the port of Ostia.  From there, they were sent by barges, up the Tiber to Rome where they were dragged to the construction site for erection.

The dome was originally covered in bronze and there are reports from travelers of it sparkling in the sunlight, the glint playing on the surrounding skyline.  However during the middle ages most was pilfered, sometimes with official sanction, sometimes not, the shortage of building materials often acute.  The last of it, Pope Urban VIII (Maffeo Barberini, 1568–1644, pope 1623-1644) in 1631, needing ordinance for his military campaigns to expand the borders of the Papal States, stripped what bronze remained as well as that from the portico to melt down for cannons.  Romans, as cynical about their rulers then as now, were soon sharing the saying “quod non fecerunt barbari, fecerunt Barberini” (what was not done by the barbarians, was done by the Barberini).

The ass's ears, circa 1860.

Roman architect and Engineer Marcus Vitruvius Pollio (circa 75-10 BC) wrote the influential De architectura which defined the building and aesthesis standards of Classical architecture and the design of the Pantheon follows his rules, height and width exactly match, meaning a perfect sphere would precisely fit inside the dome.  Vitruvius would not have been best pleased at the additions made in the 1600s by Urban VIII.  Sometimes wrongly blamed on Bernini, pontiff turned amateur architect added two bell towers to the sides of the façade which, although disliked by Romans who nicknamed them le orecchie del culo (the ass’s ears), it wasn’t until late in the nineteen century they were finally demolished.

The Pantheon, Rome.

The oculus in the Pantheon is the most famous of the many built by the Romans.  Open to the weather, it allows rain to enter and fall to the floor, where it is carried away through drains. A masterpiece of Roman architectural scale, though it looks small, the oculus’ diameter is 27 feet (8.2m) allowing it to light the building as the sun lights the earth and rain also keeps the building cool during the hot summer months.  A clever trick of lighting (and mathematics) was played out on every 21 April, the founding date of Rome.  At midday, the sunlight hits the metal grille above the door, filling the entrance way with light, timed to coincide with a ceremony at which the emperor appears in the space, reflecting his status as either an earthly god on one on whom the blessings of the gods shone.  Which of these applied depended on the Emperor.  In style, if not scale, the Pantheon was the inspiration for the Große Halle (Great Hall (and referred to in contemporary documents also as the Volkshalle (People's Hall or Ruhmeshalle (Hall of Glory)) which was to be the centrepiece of Germania as Berlin was to be re-named upon becoming the capital of the Third Reich.

Albert Speer's (1905–1981; Nazi court architect 1934-1942; Nazi minister of armaments and war production 1942-1945) post-war memoirs (1969) are not wholly truthful but on matters of architecture they are thought reliable and provide an insight not only into the grandiose plans but also the political and psychological aspects of representational buildings to which Adolf Hitler (1889-1945; Führer (leader) and German head of government 1933-1945 & head of state 1934-1945) attached such importance.  The monumental size alone was significant and despite Hitler being scornful of the mystical notions of some of his paladins, Speer was convinced that inherent in the awe-inspiring scale of the designs was the idea of them becoming places of worship, something which would be reinforced as they aged, unchanged, over the centuries.  Able to accommodate 150-180,000 people, the dome would have had a diameter of 250 metres (825 feet). rising in a slightly parabolic curve to a height of 221 metres (726 feet) while the oculus would be 46 metres (152 feet) in diameter, larger than the entire dome of either the Pantheon (43 metres (142 feet)) or that of St Peter's Basilica (44 metres (145 feet)).  The interior would be 16 times the volume of St Peter's.

Model of the Great Hall intended for Germania.

Speer also noted that even in the late 1930s when first he showed the architectural drawings to Hitler, the Führer suspended belief in facts when it suited him.  Because it was technically possible, Speer originally envisaged building the dome without the use of any structural steel but Hitler objected that were it to be struck by a bomb, the vaulting might be so damaged that without a supporting framework, repairs would be impossible.  Speer conceded the point but when he had questioned whether it was wise to have so tall a structure build in the very heart of the Reich's capital where it would act as a navigational aid for attacking bombers, Hitler breezily replied that Hermann Göring (1893–1946; leading Nazi 1922-1945, Hitler's designated successor & Reichsmarschall 1940-1945) had assured him his Luftwaffe would ensure "no enemy plane will ever enter Germany's skies".  Infamously, the Reichsmarschall would boast to the German people: "If as much as a single enemy aircraft flies over German soil, my name is Meier!"; the Royal Air Force's (RAF) bombing raids on Berlin soon began.

Lindsay Lohan with peacock feathers. during blonde phase.

The eye-like feature on a peacock's tail-feathers are called an oculus and because the collective noun for a group of peacocks (peafowl) is "an ostentation" so these several could be styled "an ostentation of oculi".  This photograph is available as a 2024 calendar.