Concept
Rarefaction
Overview
Rarefaction is the reduction of an item's density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave (see picture).
Rarefaction waves expand with time (much like sea waves spread out as they reach a beach); in most cases rarefaction waves keep the same overall profile ('shape') at all times throughout the wave's movement: it is a self-similar expansion. Each part of the wave travels at the local speed of sound, in the local medium. This expansion behaviour contrasts with that of pressure increases, which gets narrower with time until they steepen into shock waves.
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 Rarefaction is discussed.
VII. That rarefaction cannot be intelligibly explained unless in the way here proposed. And indeed I am unable to discover the force of the reasons which have induced some to say that rarefaction is the result of the augmentation of the quantity of body, rather than to explain it on the principle exemplified in the case of a sponge. For although when air or water is rarefied we do not see any of the pores that are…
René Descartes, Selections from the Principles of Philosophy
names the idea; states what it is
Therefore some other substance must be added to matter, either by creation, or by something else being changed into it. Consequently no matter can be multiplied save either by rarefaction as when air is made from water; or by the change of some other things, as fire is multiplied by the addition of wood; or lastly by creation. Now it is manifest that the multiplication of matter in the human body does not occur by…
Aquinas Thomas, Summa Theologica, Part I
states what it is; names the idea
The immense rarefaction of explosive bodies by heat, depends either on the escape of air before condensed in them, or on the expansion of the constituent parts of those bodies. This distinction has not been sufficiently considered by any one to my knowlege; nor shall I at present amuse the Society upon this head; it being enough for my present purpose to observe, that they may be thus…
Various, Philosophical transactions, Vol. L. Part I. For the year 1757.
names the idea; opens on it
Thus, a habit is a habit of something, knowledge is knowledge of something, attitude is the attitude of something. So it is with all other relatives that have been mentioned. Those terms, then, are called relative, the nature of which is explained by reference to something else, the preposition 'of' or some other preposition being used to indicate the relation. Thus, one mountain is called great in comparison with…
Aristotle, The Categories
states what it is; author linked in the graph
This cause was afterward ascertained, deductively, to be the rarefaction of the air, occasioned by the increase of temperature as the day advances.
John Stuart Mill, A System of Logic, Ratiocinative and Inductive
states what it is; names the idea
Philosophers who discussed Rarefaction
Related ideas
Place in the tradition
Part of Anaximenes of Miletus.