3. As a _Concave Speculum_ reflects the Object _bigger_, more obscure and _Inverted_: So a _Concave Corpus Obstans_ ecchoes back the Sound (insensibly) _bigger_, _slower_ (though _stronger_) and also _inverted_; but never according to the order of Words. Nor do I think it possible for the Art of Man to contrive a _Single Eccho_, that shall invert the Sound, and repeat backwards; because then the Words last spoken, that is, which do last occur to the _Corpus Obstans_, must first be repell'd; which cannot be: For where, in the mean time, should the first Words hang, and be conceal'd, or lie dormant? Or how, after such a pause, be reviv'd and animated again into Motion? Yet in complicated or _Compound Ecchoes_, where many receive from one another, I know not whether something that way may not be done. From the determinate _Concavity_ or _Archedness_ of these reflecting Bodies, it comes to pass, that some of them, from a certain distance or posture, will eccho back but one determinate Note, and from no other place will they reverberate any; because of the undue Position of the sounding Body. Such an one (as I remember) is the Vault in _Merton_ College in _Oxford_. 4. As a _Speculum_ takes in and reflects more of its Object, when plac'd at a great distance from it, than when nearer; because it reflects according to the apparent Magnitude of the Body at such a distance, which is less: So also the _Ecchoing Body_, being remov'd farther off, reflects more of the Sound, than when nearer. And this is the reason, why some Ecchoes repeat but one Syllable, some one Word, and some many. 5. As _Specula's_ may be so plac'd, that reflecting one upon or into the other, either directly or obliquely, one Object shall appear many; as in Sir _Samuel Moreland_'s Glass-room: After the same manner _Ecchoing Bodies_ may be so contriv'd and plac'd, as that reflecting the Sound from one to the other, either directly and mutually, or obliquely and by Succession, out of one Sound shall many Ecchoes be begotten; which in the first case will be all together, and somewhat involv'd or swallow'd up of each other, and thereby confus'd (as a Face in Looking-glasses obverted) in the other they will be distinct, separate, and succeeding one another; as most _multiple Ecchoes_ do. Moreover a _Multiple-Eccho_ may be made, by so placing the _Ecchoing Bodies_, at unequal distances, that they reflect all one way, and not one on the other; by which means a manifold successive Sound will be heard (not without astonishment) one Clap of the hands like many, one Ha, like a laughter, one single Word like many of the same Tone and Accent, and so one Viol like many of the same kind imitating each other.