Your desire is to know, why sound is louder in a Vault, and in a large Room then in a less? I answer, A Vault or arched Figure is the freest from obstruction, as being without corners and points, so as the sensitive and rational corporeal motions of the Ear can have a better perception; like as the Eye can see farthest from a hill then being upon a level ground, because the prospect is freer from the hill, as without obstruction, unless it be so cloudy that the clouds do hinder the perception; And as the eye can have a better prospect upon a hill, so the ear a stronger perception in a Vault; And as for sound, that it is better perceived in a large, then in a little close room or place, it is somewhat like the perception of sent, for the more the odorous parts are bruised, the stronger is that perception of sent, as being repeated double or treble, which makes the perception stronger, like as a thick body is stronger then a thin one; So likewise the perception of sound in the air; for though not all the parts of the air make repetitions, yet some or many make patterns of the sound; the truth is, Air is as industrious to divulge or present a sound, by patterns to the Ear, as light doth objects to the Eye. But then you may ask me, Why a long hollow pipe doth convey a voice to the ear more readily, then any large and open place? My answer is, That the Parts of the air in a long pipe are more Composed and not at liberty to wander, so that upon necessity they must move onely to the patterning out of the sound, having no choice, which makes the sound much stronger, and the perception of the Ear perfecter; But as for Pipes, Vaults, Prospects, as also figures presented in a room through a little hole, inverted, and many the like, belongs more to Artists then to my study, for though Natural Philosophy gives or points out the Ground, and shews the reason, yet it is the Artist that Works; Besides it is more proper for Mathematicians to discourse of, which study I am not versed in; and so leaving it to them, I rest, Madam, _Your faithful Friend_ _and Servant._ XXVIII. _MADAM,_