The word “air” occurs in the text over 200 times, but not always as a translation of the same Latin word. With a term so elastic and so ambiguous it would have been mere pedantry to attempt a uniform rendering; and indeed such uniform rendering would have been more misleading than the course adopted of rendering according to the context, which the idiom of our language seemed to demand. Seneca has two main terms for air--_aër_ and _spiritus_. _Aër_ means, generally speaking, either air generically, or the atmosphere specifically. _Spiritus_, on the other hand, denotes air under certain conditions of tension, or strain, or pressure, when it is capable of exerting force or violence; to its influence are attributed many effects due in reality to gases, or other causes. On p. 52, l. 1, we have the definition “air (_spiritus_) is the atmosphere (_aër_) in violent motion”; and on p. 205 the concluding words of V. xiii. are “air differs from wind in degree alone. A more violent air is a wind; air in turn is gently flowing atmosphere,” where again _spiritus_ is “air” and _aër_ “atmosphere.” Again, in the _Aetna_, l. 212, we read, “The winds when inflated are called _spirit_; when in subsidence, _air_” (Professor Ellis’s translation), where the same terms _spiritus_ and _aër_ are employed.[123] [123] For a discussion of the meaning of the term _spiritus_ and the parallelisms in its use by Seneca and the author of the _Aetna_, see Professor Ellis’s edition of that poem, Prolegomena, pp. xl-xliii. Now if our author had been consistent in the use of the words, there would have been a strong case for a uniform adoption of “air” and “atmosphere,” whenever they occurred. But numerous passages might be cited to show that he interchanges the words without apparent motive, just as we do “air” and “atmosphere.” For example, on p. 69, l. 2, “So fire will pass into air (_spiritus_),” while on p. 71, l. 9, “the air (_aër_), which is interchangeable with fire.” Again, on p. 75, l. 6, “When the clouds have enclosed air” (_spiritus_); l. 26, “atmosphere (_aër_) shut up in a hollow cloud.” A still more conclusive case, though the passage is probably in other respects corrupt, occurs in the last sentence of c. xxix. p. 77, where the first “air” is _spiritus_, the second, a mere synonym or variant, is _aër_. Cf. p. 187, l. 27, and the passages cited below from pp. 245, 249, 251, 259, 260. The translator has little choice. He must follow his author, and, where the latter makes a distinction, must endeavour to reproduce it; otherwise he must, as the author did, observe the idiom of his own language. In accordance with this principle _aër_ is usually translated “atmosphere,” and _spiritus_ “air”; but circumstances have rendered unavoidable a considerable number of exceptions.