This constellation, HorologiumOscillatorium, was added by La Caille in 1752 to honor Christiaan Huygens who invented the first pendulum clock in 1656, based on the pendulum introduced by Galileo Galilei. The time-pieces previously in use had been balance-clocks, Chris Huygens’ pendulum clock was regulated by a mechanism with a ‘natural’ period of oscillation and had an error of less than 1 minute a day, the first time such accuracy had been achieved []. Huygens is also famous for discovering Saturn’s rings. Horologium was also the term used for a sun-dial in ancient Roman times. And in ancient Greece orologion was a name given to various instruments by means of which the ancients measured the time of the day and night.

Horologium is from Latin horologium, from Greek orologion, literally ‘that which tells the hour’, from ora, ‘hour’, and –logion, that which tells, from legein to tell. Greek ora, hour, comes from the Indo-European root *yér ‘Year, season’. Derivatives: year, Yahrzeit (the anniversary of the death of a relative, observed with mourning and the recitation of religious texts), horary, hour, horologe (a device, such as a clock or sundial, or watch, used in telling time), horology (the science of measuring time, the art of making timepieces), horoscope, (these words from Greek hora, season). [Pokorny 1. ei– 293. Watkins

“A clock (horologia) is so called because there ‘we read the hours’ (horaslegere), that is, we deduce them. It is set up in sunny places, where the shadow from the gnomon runs across the incised lines to show what hour of the day it is” [p.404]. “’Drawers of horoscopes’ (horoscopus) are so called because they examine (speculari) the times (hora) of people’s nativities with regard to their dissimilar and varied destiny.” [p.183.] [The Etymologies of Isidore of Seville, 7th century AD]

In Greek mythology, the Horae (‘the Hours‘), were goddesses of time, variously the year, seasons and the hours of the day; “Horae, those embodiments of the right moment— the rightness of Order unfolding in Time” []. The course of the seasons (or hours) is symbolically described by the dancing Horae, following each other in measured steps, they are an emblem of fleeting time. They stand around the throne of Zeus, and their regular occupation is to open and shut the gates of Olympus (Heaven), and yoke the steeds to the chariot of the Sun. In works of art the Horae were represented as blooming maidens, carrying the different products of the seasons. The number of the Horae is different in the different writers, though the most ancient number seems to have been two, as at Athens; but afterwards their common number is three, and another group of twelve Horai (or Horae) were goddesses of the hours of the day. []. Janus says “I sit at Heaven’s Gate with the gentle Hours”. (Janus might be adjacent Dorado and Horologium is also adjacent to Caelum, the celestial realm].

“The twelve Horai (or Horae) were goddesses of the hours of the day and perhaps also of the twelve months of the year. They oversaw the path of the sun-god Helios as he traveled across the sky, dividing the day into its portions. The ancient Greeks did not have hours of fixed length like we do today. Instead they divided the hours of daylight into twelve portions, identified by the position of the sun in the sky. Thus the length of the hour varied between the longer days of summer and shorter ones of winter. The twelve Horai were not always clearly distinguishable from the Horai of the seasons, who were also described as overseeing the path of the sun” http://www.theoi.com/Titan/Horai.html

The constellation HorologiumOscillatorium is on the banks of the river Eridanus and also in a position to be at the mouth of that river, and if Hydrus (also adjacent) is the ocean (Oceanus), Horologium could also be on the shore of that ocean:

“It is the extreme limit of brevity of the hour’s segments, when one instant stops and another starts. Hour (hora) is a Greek term (compare ora), but it is pronounced in the same way in Latin. The hour is the boundary of time, just as the word ora means a boundary like the shore of the sea, or the bank of a river, or the border of a garment.” [The Etymologies of Isidore of Seville, 7th century AD, p.125.]

Latin ora, is plural of os¹, margin, border, a mouth, or an opening, it is related to the word oral, meaning mouth, from the Indo-European root *ós ‘Mouth’. Derivatives: oral, os¹, oscillate, osculate (to kiss, come together, contact), osculum (the mouthlike opening in a sponge), ostiary (a church doorkeeper), ostium (a small opening or orifice), usher (from ostium, door, a doorkeeper), inosculate (to make continuous; blend), orifice, orotund (orotund talk, full in sound; sonorous: orotund tones), oscitancy (yawning), peroral (through the mouth). [Pokorny 1. ous– 784. Watkins

Oscillate literally refers to a steady back-and-forth motion, as that of a pendulum. The pendulum clock was originally called Horologium Oscillatorium, as was the name of this constellation before it was shortened to Horologium.

In a passage in the Georgics, Virgil applies the word oscillum to a small mask of Bacchus hung from trees to move back and forth in the breeze. From this word oscillum may have come another word oscillum, meaning ‘something, such as a swing, that moves up and down or back and forth.’ And this oscillum was the source of the verb oscillare, ‘to ride in a swing,’ and the noun (from the verb) oscillatio, ‘the action of swinging or oscillating.’ The next time one sees something oscillating, one might think of that small mask of Bacchus swinging from a pine tree in the Roman countryside. [American Heritage Dictionary

Haruspices are so named as if the expression were ‘observers (inspector) of the hours (hora)’; they watch over the days and hours for doing business and other works, and they attend to what a person ought to watch out for at any particular time. They also examine the entrails of animals and predict the future from them.” [The Etymologies of Isidore of Seville, 7th century AD, p.182.]

Latin Haruspices comes from the Indo-European root *ghere- ‘Gut, entrails’. Derivatives: yarn, hernia (a rupture), chord² (the string of a musical instrument), cord (also spinal cord), cordon, harpsichord, hexachord, tetrachord, (from Greek khord, gut, string), chorion (the outer membrane enclosing the embryo, from Greek khorion), haruspex (a priest in ancient Rome who practiced divination by the inspection of the entrails of animals, from Latin haruspex, ‘he who inspects entrails’). [Pokorny 5. gher– 443. Watkins

The horae were daughters of Zeus and Themis, goddesses of the seasons. These may have been the:

Nymphs believed to be daughters of Zeus and Themis lived in a cave on the river Eridanus [Apollod. ii. 5. § 11; Schol. ad Apollon. Rhod. iv. 1396; Hesych. s. v. Themistiades http://www.theoi.com/Titan/TitanisThemis.html ] This constellation HorologiumOscillatorium is on the banks of the river Eridanus

© Anne Wright 2008.

Fixed stars in Horologium
Star 1900 2000 R A Decl 1950 Lat Mag Sp
zeta 01ARI05 02ARI28 039 46 33 -54 45 48 -63 39 51 5.26 F2
eta 03ARI14 04ARI37 038 56 20 -52 45 32 -61 50 53 5.26 A9
iota 06ARI50 08ARI13 040 12 50 -51 00 55 -61 00 55 5.42 G0
alpha 14TAU26 15TAU49 063 05 09 -42 25 00 -61 43 59 3.83 K1