PHYSICAL SCIENCE

CHAP.		PAGE
XIV.	There is nothing inconsistent with this in the explanation given (I. xv.) of meteors. There may be an analogy to what is observed in fires, where isolated groups of houses catch fire through the gradual accumulation of heat.	65
XV.	Some (Stoics) believe that spontaneous combustion occurs in the air.	66
XVI.	The difference between a flash of lightning and a bolt.	66
XVII.	Some explain the sound of thunder as being due to the meeting of hot and cold, similar to the effect when hot iron is plunged into water.	67
XVIII.	Anaximander A pre-Socratic Greek philosopher from Miletus. attributes these effects to air and explains all the phenomena by reference to it.	67
XIX.	Anaxagoras A pre-Socratic Greek philosopher who introduced the concept of "Nous" or mind. says it is the ether that acts on the lower atmosphere to produce them; it sends out fire.	68
XX.	Diogenes of Apollonia A Greek philosopher who believed air was the fundamental substance of the universe. thinks that fire and air interact, producing one another, as can be observed in various phenomena.	68
XXI.	Authorities are discarded in favor of an independent explanation. A flash and a bolt are fire in some form; they differ only in degree.	69
XXII.	The analogy of fire on earth must apply above. Lightning is due either to impact or friction. Hurricanes are a sufficient cause for the former.	70
XXIII.	Clouds and air may, through friction, also be a cause. The fires produced in this way are insubstantial and vanish quickly.	71
XXIV.	Fire, by reason of its lightness, rises, just as water settles due to its weight. But in the case of a lightning bolt, it is forced down, contrary to its nature, like a "weeping" tree Referring to the downward bending of branches or sap movement..	71
XXV.	But it is said that wet clouds produce fire. How?	72
XXVI.	There is no inconsistency in the combination of potential fire and water within the same cloud. A log burns at one end while exuding moisture at the other. On two occasions, an island was thrust up by fire in the Aegean Sea, with fire overcoming water. In fact, clouds are required for lightning; any exceptions to this are only apparent.	72
XXVII.	Different kinds of thunder. The growling and the crashing sounds, with their causes.	75
XXVIII.	For thunder to sound, clouds of a particular shape must meet in a particular way. A bladder does not burst with a report if it is cut; a broad, simultaneous blow over the whole cloud is necessary for an explosion.	76
XXIX.	The proper shape and the rupture of the cloud are necessary. Compare this to drums, etc.	77
XXX.	According to some, clouds are not necessary for thunder: witness the eruptions of Etna and the overthrow of the army of Cambyses King of Persia, son of Cyrus the Great., where particles of sand were the medium for the thunder and lightning. But in this case, a cloud was likely formed—denser and more solid than one composed of mere air—before the sound was emitted.	77
XXXI.	The strange effects of lightning.	78
XXXII.	Portents and events: their undoubted and widespread connection.	79
XXXIII.	Thunderbolts. The threefold division of the art of interpreting them.	81