...all to mind the prevalent belief that fog, snow, hail, and rain, indeed, any conditions of the atmosphere that render it optically opaque, render it also acoustically opaque; which, up to the time of Mr. Tyndall 's experiments in the English Channel, off Dover, had scarcely been questioned. His tests made in 1873-74 proved conclusively, as is now well known, that on clear days the air may be composed of dif...