Now as any Object (a Man for example) seen through a thicken'd Air, by _Refraction_ appears greater than really he is: So likewise a _Sound_, heard through the same thicken'd part of the _Atmosphere_, will be considerably vary'd from what it would seem to be, if heard through a thinner Medium. And this I call a _Refracted Sound_: But what this Refraction of Sound is, and how caus'd, may hereafter be discuss'd, when the Nature, and Motion, or Progression of Sounds are well stated. For the Improvement of _Refracted Vision_ artificial Instruments have been made, by grinding or blowing Glasses, into a certain Figure, and placing them at due distances, whereby the Object may be (as 'twere) enabled to send forth its Rays more vigorously, and the Visive Faculty impower'd the better to receive them. And thus also Instruments may be contriv'd for the assisting both the _Sonorous Body_, to send forth its Sound more strongly, and the _Acoustick Faculty_, to receive and discern it more easily and clearly. _For_, 1. As a fine _Glass Bubble_, fill'd with clear Water, and placed before a burning Candle or Lamp, does help it to dart forth its Rays to a prodigious Length and Brightness: So an _Instrument_ may be invented, that apply'd to the Mouth (or any Sonorous Body) shall send forth the Voice distinctly to as prodigious a Distance and Loudness. For if the _Stentoro-phonecon_ (which is but a rude and unartificial Instrument) does such great feats, what might be done with one compos'd according to the Rules of Art? whose make should comply with the Laws of _Sonorous Motion_ (which that does not) and therefore not so much _Refract_, as to alter and confound the _Tone_ of the _Voice_ and Words (as that somewhat does.) Now of what use such an Instrument might be for speaking clearly and articulately at a distance (and that without altering the Tone of the Voice) whether it be at Sea or at Land (but especially at Sea in tempestuous Weather and in the Night) is obvious to any Man to conceive. 2. As Instruments have been invented to help the Eye, So likewise are there some, and more such there may be, for the Ear. _For_, 1. As _Spectacles_ and other _Glasses_ are made to help the _Purblind_ and weak _Eyes_, to see at any competent distance: So there are _Otacousticks_ (and better may be made) to help weak _Ears_ to hear at a reasonable distance also. Which would be as great a help to the infirmity of Old Age, as the other invention of Spectacles is, and perhaps greater; forasmuch as the Hearing what's spoken is of more daily use and concern to such Men, then to be able to _read Books_ or to _view Pictures_.