On the one hand we have the problem (reverberation) which we have been discussing up to the present moment, and on the other the whole Question of the transmission of sound from one room to another, through the walls, the doors, the ceiling and the ?oors; and the telephonic transmission, if I may so call it, through the length of the structure. It is five years ago since this second problem was first attacked and though the research is certainly not complete, some ground has been covered. A quantitatively exact method has been established and the transmission of sound through about twenty different kinds of partitions has been determined. For example: Transmission of sound through four kinds of doors has been studied; two of oak, two of pine, one of each kind was paneled and was relatively thin and light; one of each kind was very heavy, nearly four centimetres thick; through four kinds of windows, one of plate glass one with common panes, one double with an air space of two centimetres between, one with small panes set in lead such as one sees in churches; through brick walls with plaster on both sides; through walls of tile similarly plastered; through walls of a character not common in France and which we call gypsum block; through plaster on lath; through about ten different kinds of sound insulators, patented, and sold in quantities representing hundreds of thousands of dollars each year, yet practically without value, since one can easily converse through six thicknesses of these substances and talk in a low tone through three, while a single thickness is that ordinarily employed. The behavior of an air space has been studied, the effect of the thickness of this air space, and the result of filling the space with sand, saw-dust and asbestos. In spite of all this, the research is far from complete and many other forms of construction must be investigated before it will be possible to publish the results; these determinations must be made with the greatest exactness as very important interests are involved.
