The final book of this work focuses on various meteorological and geological phenomena; like the cosmic phenomena of Book V, the purpose of Lucretius’ arguments here is to dispel belief in the gods’ involvement. It ends, rather abruptly, with an explanation of pestilence.

Beginning with meteorology, Lucretius addresses thunder, which strikes fear into the hearts of the ignorant. There are several causes for this loud noise, according to Lucretius. Sometimes, it’s caused by the sound of clouds colliding; since they are somewhat dense, they make a noise when they crash together. Sometimes, too, an air pocket forms inside a cloud, and the sound of it popping creates the sound of thunder. Thunder can also be the sound of lightning being extinguished rapidly, or igniting a cloud.

From thunder Lucretius moves on to lightning. One cause of lightning is the collision of clouds: “The process is similar to that when stone strikes stone or iron; for in that case, too, light leaps out, scattering glowing sparks of fire” (Book VI, lines 161-163; page 183). When air pockets in clouds burst, too, they can spark a bolt of lightning. Regarding the formation of thunderbolts, Lucretius believes that they are honed by the wind inside the clouds.