1. The Italian is discorso, or ‘mental discourse’.

2. That is, he is talking about what happens in the atmosphere, not referring to how air behaves when trapped in the earth or water, which are not its ‘proper regions’.

3. I assume that ‘sonority’ is the quality of the source of the sound, and ‘transonority’ is the quality of the medium through which it is transmitted.

4.Actually he says ‘arrows’, which doesn’t make sense. Perhaps he is using an obsolete dialect word which has escaped the attention of even the largest Italian dictionary.