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.
2. As Perspective-Glasses and Telescopes help the Eye to see Objects at a very great distance, which otherwise would not be discernable; in like manner may a sort of Otacousticks be so contriv'd, as that they shall receive in Sounds made at a very great distance also, but with so much advantage, that the Ear shall be able to hear them, which otherwise would have been inaudible.
And these Otacousticks in some respects would be of greater use than Perspectives. For whereas at Land Perspectives are many times render'd almost useless, by the interposition of Woods and Mountains, which hinder the Sight from reaching very far: Our Otacousticks would, notwithstanding these Obstacles, take in a Sound made some Leagues off. Which might be of notable use in the time of War, for discovering the Enemy at a good distance, when he marches or lyes incamp'd behind a Mountain or Wood, or any such place of shelter.
Yea, even at Sea also, where Perspectives are of most use, by reason of the plainess of the Surface of the Water; yet sometimes there Otacousticks may be of more benefit, when in dark hazy Weather the Air is too thick, or in Stormy Tempestuous Weather the Waves arise too high for the Perspective to be made use of.
But, whether at Sea or Land, Perspectives become altogether insignificant in the Night-time (unless it be for viewing the Stars) which is the chief time for using Otacousticks; as it is generally, for Soldiers to take their March, when they would surprise their Enemies.
And therefore this sort of Otacousticks have then their chief use, when Perspectives are of no use at all; besides that they may be imploy'd in the Day-time, as well as Perspectives, whence they may (not unfitly) be term'd the most useful Instrument of the two.
3. As Microscopes or Magnifying-Glasses help the Eye to see near Objects, that by reason of their smallness were Invisible before; which Objects they Magnify to a strange greatness: So Microphones or Micracousticks, that is Magnifying Ear Instruments, may be contriv'd after that manner, that they shall render the most minute Sound in nature distinctly audible, by Magnifying it to an unconceivable loudness.