Dialogues. Consolation to Helvia ; On tranquillity of mind ; On the shortness of life -- Letters. Letter 24 ; Letter 57 ; Letter 79 ; Letter 110 -- From Natural questions. I Praef. 1-10 (Seneca urges Lucilius to enjoy the inspiration and benefits of philosophical study) ; 4A.2.4-6 (The cataracts of the Nile) ; 6.1.4-7 (The terrors of earthquakes).