that is, such apparatus as is com- transparency, and, in spite of this, not making them mouth is employed as a resonator, and an ordinary monly employed in acoustical experiments. A very adhere to other paper. Paper cannot be attached to tea bell as the source of sound. The tuning is effected… … held over the mouth of the paper tube, and the dia- Fig. 1—RE-ENFORCEMENT OF VOCAL SOUNDS. phragm is moved up or down in the tube until a po- sition is reached in which the bell will yield a full tone, may be strengthened by a confined body of air is which is much louder than it is capable of…
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![An illustration from The Telegrapher [microform] (1864)](https://img.insideoutlibrary.com/img/200/ia-telegrapher05nati-320-204.webp)
