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.
- 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