Concept
Second
Overview
The second (symbol: s) is a unit of time derived from the division of the day, first into hours, then into minutes, and lastly into seconds, for a total of 24 × 60 × 60 = 86400 seconds per day. That definition, based on 1⁄86400 of a rotation of the Earth, is still used by the Universal Time 1 (UT1) system.
The current and formal definition in the International System of Units (SI) is more precise:The second [...] is defined by taking the fixed numerical value of the caesium (Cs) frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the Cs-133 atom, to be 9192631770 when expressed in the unit hertz, which is equal to s−1.
This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with caesium clocks. As the speed of Earth's rotation varies and is slowing ever so slightly, a leap second is added at irregular intervals to civil time to keep clocks in sync with Earth's rotation.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Second is discussed.
The motion of the second is controlled by the first, and hence the oblique line in which the planets are supposed to move becomes a spiral. The motion of the same is said to be undivided, whereas the inner motion is split into seven unequal orbits—the intervals between them being in the ratio of two and three, three of either:—the Sun, moving in the…
Plato, Timaeus
states what it is; names the idea
the nobleness of her soul, relating some of her virtues proceeding from her soul; in the second, I speak of her as regards the nobleness of her body, narrating some of her beauties: here, “Love saith concerning her.” This second part is divided into two, for, in the first, I speak of certain beauties which belong to the whole person; in the second, I speak of certain beauties which belong to a distinct part of the…
Dante Alighieri, The New Life
names the idea; states what it is; opens on it
The second consisted of those little globules that were formed by the rubbing off of the first. The interstices betwixt these globules of the second element was filled up by the particles of the first. But in the infinite collisions, which must occur in an infinite space filled with matter, and all in motion, it must necessarily happen that many of the globules of the second element should be broken and grinded down…
Adam Smith, The Essays of Adam Smith
names the idea; opens on it
Now, there are four first principles of all things, the first of life, the second of motion, the third of birth, the fourth of death. The first is linked to the second by Unity, in the Unseen: the second to the third by Mind, in the sun: the third to the fourth by Nature, in the moon. Over each of these combinations a Fate, daughter of Necessity, presides, and holds the keys; of the first Atropus, of the second…
Plutarch, Selected Essays of Plutarch, Vol. II.
names the idea; opens on it
But this is a false inference. Hence, where the first thing is untrue, it is quite unnecessary, provided the second be true, to add that the first is or has become. For the mind, knowing the second to be true, falsely infers the truth of the first. There is an example of this in the Bath Scene of the Odyssey.
Aristotle, The Poetics of Aristotle
names the idea; states what it is
Related ideas
- Orpheus
- Roger Bacon
- Speed
- British Science Association
- Christiaan Huygens
- Earth's rotation
- Caesium
- Carl Friedrich Gauss
- Hyperfine structure
Place in the tradition
Part of Philosophy of physics.