1. We may presume that the trabes are, for the most part, to be referred to the aurora borealis. The chasma and the appearances described in the twenty-seventh chapter are probably varieties of this meteor. On these phænomena we have the following remarks by Seneca: "Lucem in aëre, seu quamdam albedinem, angustam quidem, sed oblongam, de noctu quandoque visam, sereno cælo, si parallelo situ sit, Trabem vocant; si perpendiculari, Columnam; si, cum cuspide Bolida, siveJaculum." Nat. Quæst. vii. 4, and again, vii. 5, "Trabes autem non transcurrunt nec prætervolant, ut faces, sed commorantur, et in eadem parte cceli collucent."

2. Seneca describes this meteor, ubi supra, i. 14. "Sunt chasmata, cum aliquando cœli spatium discedit, et flammam dehiscens velut in abdito ostentat. Colores quoque horum omnium plurimi sunt. Quidam ruboris acerrimi, quidam evanidæ et levis flammæ, quidam candidæ lucis, quidam micantes, quidam æquabiliter et sine eruptionibus aut radiis fulvi." Aristotle's account of chasmata is contained in his Meteor. lib. i. cap. 5. p. 534.