Institutio Oratoria

He will not maintain the same tone throughout his exordium, statement of fact, arguments, digression and peroration. He will speak gravely, severely, sharply, with vehemence, energy, fullness, bitterness, or geniality, quietly, simply, Hatteringly, gently, sweetly, briefy or wittily; he will not always be like himself, but he will never be unworthy of himself.