In one of the Protestant churches of our city, we were shown a sounding-board, whose authors seemed to have halted between the acoustic merits of the paraboloid and the graceful shape of the pilgrim’s scallop-shell. We were told that “it helps the voice of the preacher.” There seemed to be too much of it for ornament, if its principle be wrong or inefficient, and too little for usefulness if right. Many attempts to improve the acoustic properties of halls designed for public lectures are failures through faulty execution of correct designs.
We once saw the working-plans of a lecture-room, where the line of intersection of the end wall with the floor of the stage or platform was a _parabola_, the arch above and behind the lecturer’s desk being a _semi-paraboloid_, springing from the wall at the height of the speaker’s voice. Thus, it was supposed that the _pulses_ reflected from the walls and arch would proceed in parallel lines or “waves of sound,” because the _initial pulse_ would always be given at the _focus_ of the reflector.
The place of every joist in the cylindrical wall was carefully marked, and the dimensions and place of each rib of the paraboloidal arch accurately given. But in executing the design, the builder discovered a _mistake_!--“the floor of the stage would not be a true circular segment!” So he “_corrected_ it”--with stunning effect upon the lecturer, and to the utter confusion of his audience. And the design was pronounced _a failure_.
In looking through the work before us, we almost unconsciously began to say: “This is nothing new; we have seen this, and more than this, before.” And in the same sense, we suppose it might as well be said that _nothing_ is essentially new.
We have lately seen a notice of an invention for tracing patterns on glass by means of a _jet_ of sand. Of course, it is nothing new. The wind has been doing the same trick with the sand of the sea-shore for ages. We have seen it long ago, and often. Doubtless, the same effect has been noticed by many others. A thought of the possible utility of a process whose result was seen may have flitted through many minds, and, like the outline of a passing cloud, have been forgotten as it passed. But honestly, we never thought of tracing lace patterns on glass by any such process. And while new combinations of well-known truths give new and useful results, we hope they may never cease to be made.