Moreover, by this means, a _Weather-cock_ may be so contriv'd, as that with an ordinary blast of Wind it shall cry (or whistle) loud enough to be heard many Leagues: Which happily may be found of some use, not only for _Pilots_ in mighty tempestuous Weather, when _light Houses_ are render'd almost useless, but also for the measuring the strength of Winds, if allowance be made for their different moisture. For I conceive, that the more dry any Wind is, the louder it will whistle _cæteris paribus_; I say, _cæteris paribus_, because, besides the strength and dryness of Winds or Breath, there are a great many other things (hereafter to be considered) that concur to the increase or magnifying of Sounds, begotten by them in an Instrument exposed to their Violence, or blown into. 3. The third _Problem_, is, _That a Sound may be convey'd from one extreme to the other_ (or from one distant place to another) _so as not to be heard in the middle_. By the help of this _Problem_ a Man may talk to his Friend at a very considerable distance, so that those in the middle space shall hear nothing of what passed betwixt them. FIG. V. TAB. III. _Semiplanum Sphæræ Phonicæ seu Acousticæ._ You are to conceive that (rude) _Semiplane_, as parallel to the _Horizon_: For if it be perpendicular thereunto, I suppose the upper extremity will be no longer _Circular_, but _Hyperbolical_, and the lower part of it suited to a greater Circle of the Earth. So that the whole _Phonical_ Sphere (if I may so call it) will be a solid _Hyperbola_, standing upon a _Concave Spherical_ Base. I speak this concerning _Sounds_ made (as usually they are) nigh the Earth, and whose Sonorous _Medium_ has a free passage every way. For if they are generated high in the Air, or directed one way, the case will be different; which is partly design'd in the inequality of that Draught. _A Discourse concerning the Modern _Theory_ of _Generation_, by Dr. _George Garden_ of _Aberdeen_, being part of a Letter to Dr. _William Musgrave_, L. L. D. Reg. Soc. S. and by him communicated the Royal Society._