Entasis

Entasis (pronounced en-tuh-sis)

(1) In architecture, a slight convexity given to a column or tower, as to correct the optical illusion of concavity and create the perception of straight lines.

(2) In medicine and physiology, an involuntary or spasmodic muscular contraction (also called entasia (from the Greek ɛnˈteɪzɪə)).

(3) In typography & calligraphy, the thinning in the waist of a stroke, the technique used to compensate for the visual perception of a stroke with perfectly straight sides appearing slightly to bulge.

1745–55: From the Latin entasis, from the Ancient Greek ἔντασις (éntasis) (tension, straining), from εντείνω (enteínō) (to stretch or strain tight), the construct being enta, variant stem of enteínein (to stretch tight) + teínein (to stretch) + sis.  The –sis suffix was from the Ancient Greek -σις (-sis) and was attached to words in English often via Latin or French.  It was identical in meaning with the Latin –entia and the English –ing and was used (1) to form nouns of action or process (catharsis, dialysis, diagnosis, crisis etc), (2) in medicine to form nouns of condition (psoriasis, sepsis, tuberculosis, psychosis etc) and more generally (3) nouns as required (basis, oasis, thesis, stasis etc).  Entasis is a noun; the noun plural is entases.

The Entasis or Parthenon Principle

Parthenon in Athens.

In modern architecture, entasis is the application of a convex curve to a surface for aesthetic purposes.  Its best-known use is in the columns from antiquity which curve slightly as their diameter is decreased from the bottom upward.  Because no relevant documents have yet been discovered, it’s not known whether the architects in antiquity applied the technique for aesthetic effect or as an engineering technique to enhance strength.  The latter is suggested by the design principle being described by Roman architect Marcus Vitruvius Pollio (circa 75 BC–circa 20 BC) using the Greek word enteino meaning "to stretch or strain tight", suggesting some emphasis on structural strength rather than appearance.  However, until contemporary records are uncovered, their reasons for using entasis remain mysterious, hence the two-thousand odd years of conjecture.  The most celebrated construction is the Parthenon in Athens.

1964 Rolls-Royce Silver Cloud III Flying Spur; coachwork by HJ Mulliner Park Ward.

The earliest known documented view of the matter was that written by Greek mathematician and engineer Hero of Alexandria (circa 10-circa 70), is that entasis corrects the optical illusion of concavity in the columns that the human eye would create if the correction were not made.  That’s the reason Roll-Royce have always used a variation of the  technique in their upright grilles; it’s to make it appear as if built with columns of identical dimensions.

Basilica's western front of the Second Temple of Hera, a Greek temple in Paestum, Campania, Italy.

The Second Temple of Hera was built in the Doric order circa 455 BC, just north of the first.  For the visual effect of entasis to work, the convex curve has to be so slight as to be imperceptible and it's not known why the Second Temple of Hera has an entasis so pronounced it creates an obvious curvature, not an illusion of straightness.  The proportions are such that historians have speculated it must have been deliberate, presumably purely for structural strength but it's at least possible the architect was afflicted by the desire many of his modern contemporaries share: The wish to produce something "original" and "new", the reason why so many modern buildings are so unpleasing to the eye.

Lindsay Lohan in Rolls-Royce Phantom Drophead Coupé (2007-2017).  By the 1970s factory (mostly) had ceased to use the historic terms FHC (Fixed-Head coupé) and DHC (Drop-Head Coupé (DHC) although and the revival in 2007 for the Phantom Drophead Coupé proved (thus far) a nostalgic one-off.

Over the decades, the designers generally were successful in their adaptations as they were required to make the grille wider and lower but the Phantom would have benefited aesthetically if a more traditional approach had been taken with the headlamps (centre) and even hidden units (right) would have been more pleasing.  Still, twenty-first century customers seem more accommodating of stylistic innovation than earlier generations.  In 1975, when the Camargue (1975-1986) was released, the novelty of it being the first Rolls-Royce designed using exclusively metric measurements (except for the odd carry-over component) attracted little attention but there was much comment about it being the first built with anything but a perfectly vertical grille.  The Camargue's grille was slanted at a (for mid-century Rolls-Royce) rakish 7^o.

The Pantheon Temple, Rome (left) and 1985 Rolls-Royce Camargue (right).

The Pantheon's Latin inscription M·AGRIPPA·L·F·COS·TERTIVM·FECIT actually isn't all that poetic and reads like a note the draftsman might have put on the blueprint (had there then been blueprints): it translates as "Marcus Agrippa, son of Lucius, made [this building] when consul for the third time.", crediting the Roman statesman & general, Marcus Vipsanius Agrippa (circa 63 BC–12 BC) who originally commissioned the construction during his third consulship in 27 BC.  The Pantheon that stands today was rebuilt by Emperor Hadrian (Publius Aelius Hadrianus, 76–138; Roman emperor 117-138) circa 126 AD after the original structure suffered severe damage in a blaze.  Hadrian chose to retain Agrippa's inscription as a tribute (not all the emperors were narcissists).  Since AD 609, the Pantheon has been a Roman-Catholic church and is known as the Basilica Santa Maria ad Martyres (Basilica of St. Mary and the Martyrs).

Despite the popular perception, what Rolls-Royce describes as their "Pantheon grill" doesn't feature a classic entasis (slight swelling in the middle of a column to counteract the illusion of concavity), the design does incorporate a similar visual effect: there is a (very) slight curvature which in the factory's vernacular is known as the "waftline".  Although there are, understandably, many references to the grill being the "Parthenon grill" (and there is a well-reviewed Greek restaurant in Murfreesboro, Tennessee called the Parthenon Grille), the factory has never used the term and say the designed was inspired by "Rome’s imposing Pantheon temple", a structure "...purposefully built with wider middle sections so the human eye perceives each long pillar to be completely straight."  What the architects of Antiquity did was use use an optical illusion as a "corrective" to achieve perfect visual symmetry and the Rolls-Royce engineers replicated the approach, the grill's columns wider towards the edges.  The waftline is used elsewhere, notably the gentle, upswept sweep along the sill-line which Rolls-Royce says "creates a powerful, poised stance and makes the car appear to be moving when stationary...", creating the impression of "calm perfect motion and accelerating quickly without fuss".  They clearly like the word "waft" because they coined the neologism "waftability" which is said to be "the essence of the brand".

The math of entasis.