auditorium will be of benefit for faulty acoustics, or, if this fails, that a sounding board over the speaker's head will remedy matters, Also, concerning sound-proofing in buildings, an impression prevails than an effective wall is one containing air spaces. These popular conceptions are not altogether supported by the facts. People who regard the problem with a degree of seriousness realize that the action of sound is not a matter of chance, but that the phenomena must accord with scientific laws.

In the bulletin mentioned, the results are given of a survey of the subject of sound insulation in buildings from three standpoints the theory of the subject, experimental investigations and practical installations of sound-proofing. This information thus collected while drawn from different sources and apparently unrelated, proved quite concordant and led to conclusions concerning effective sound insulation.

Two Types of Sound in Buildings. Two types of sound should be considered in the problem of insulation in buildings. One type includes sounds that are generated in the air and that progress through the air to the boundaries of the room; the other is composed of compressions generated in the building structure by motors, elevators, and street traffic.

Insulation of Sounds in Air. Sounds of moderate intensity such as those generated by the human voice or a violin may be stopped with comparative ease if the walls of the room are continuous and fairly rigid. The more vigorous sounds of a cornet, trombone, etc., would require especially heavy walls or else double partitions. Any breaks in the walls for ventilators, pipes, or doors should be guarded by effective insulation.

Insulation of Building Vibrations. Compressional waves generated in the building structure pass readily along the continuity of solid materials, and, as they have more paths for escape, are more difficult to insulate than sounds in air. Moreover, they may create trouble when they cause a wall or floor to vibrate. The insulation is based on the same procedure as that used for air sounds; namely, to interpose a new medium differing in elasticity and density. An air space in masonry would be effective if not bridged over by solid material, but since this is impossible for ordinary building constructions as the weight of bodies necessitates contact for support, an approximate insulation is sought by using air-filled substances like dry sand, ground cork, hairfelt, or flax, that possess but little rigidity but are capable of sustaining a floor or a partition that is not too heavy.

Transmission of Sound. Sound waves in air may be transmitted through an obstructing medium in three ways. First, they may pass through the air spaces of a porous material. Second, they may be transmitted by modified waves in the new medium. In this process sound compressions and rarefactions progress rapidly through the air, moving the molecules successively as they pass in somewhat the same way as a gust of wind blows the separate stalks in a wheat field. On reaching a solid partition the forward motion is hindered, particularly if the molecules of the new material are massive and resist compression. In this case most of the energy is reflected and only a small proportion progresses through the wall. On meeting a further discontinuity of material, such as wood or air, the waves are again affected, until finally a part of the energy emerges. Third, sound may be transmitted by setting a partition as whole in vibration. The partition then acts as an independent source of waves, setting up compressions and rarefactions on the further side and giving a sort of fictitious transmission. If the partition is rigid and massive the vibrations are small and very little sound is transmitted; if the partition is thin and flexible a considerable amount of energy is transferred. Usually in building constructions the partitions are complex, as for example plaster on wood lath and studding. In this case the plaster areas between the studding act in a manner similar to drum heads and transmit sound. Hard plaster on wire lath presents a different surface with a modified action on the incident sound. The transmission of sound involves a number of phenomena and is not a simple matter. It depends essentially on the character of the structure through which sound is transmitted and can be calculated only for simple cases of homogeneous materials of known constants.

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The systematic survey of the subject of sound-proofing as given in the Bulletin leads to several practical conclusions.

Ventilation System. Especial attention should be paid to the ventilation system. All effective sound-proof constructions either omit entirely a ventilation system or else construct it in some special manner to avoid transmission of sound. In some buildings air is supplied and withdrawn from rooms by individual pipes that are small in diameter and extend without break from the air supply chamber to the rooms. This results in considerable Rayleigh, Lord. Theory of Sound, loc cit. see also: Jager, G. Zur Theorie des Nachhalls, Sitzungber. der Kaisl. Akad. der Wissenschaften in Wien. Math. Natur. Klasse, Bd. CXX, Abt. 2a, 1911.

friction between the walls of the pipes and the air, with a resultant weakening of the sound waves. Without some efficient control of the transference of sound through the ventilation system it is a waste of effort to construct sound-proof walls, double doors, and other contrivances for insulation.

Sound Proof Partitions. Partitions between rooms should be as rigid and free from air passages as possible. For effective sound-proofing of a group of rooms, the partitions, floors, and ceilings between adjacent rooms should be made continuous and rigid. Any necessary openings for pipes, ventilators, doors, and windows should be placed in outside or corridor walls where a leakage of sound will be less objectionable.

Absorption of Sound. The absorption of sound is an essential feature for sound-proofing. Reflecting sound and scattering it still leaves it with energy. It must be absorbed; that is, converted into heat energy by friction, before it is eliminated as sound. This means that carpets, furniture, draperies, etc., should be present, or if greater absorption is desired, hairfelt or similar materials must be installed.

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Sound-proofing a Building. When sound-proofing a building all details should be considered with respect to the likelihood of transmission of sound. Each room, as far as possible, should be made an insulated unit by means of air spaces or air-filled materials that separate it from surrounding walls. Pipes and ventilators should be so installed as to minimize the chance of transfer of sound. Patent doors are now available that will close the door space at top, sides and bottom. In case a troublesome sound is generated in the room, it may be minimized by installing absorbing material on the walls.

The insulation of sound is a complex problem and a successful solution is obtained only when all the possibilities of transfer of sound are anticipated and guarded against. While many things may be learned from further experience and much may be gained from additional theory, enough has been revealed to give encouragement to the belief that sound-proofing may be prescribed in the future with some of the certainty that now attends the acoustic design of auditoriums.

"Sound-proofing a Building," Architectural Forum, November, 1921..

RESEARCH IN PHYSICS

CONDUCTED BY HOMER L. DODGE,

University of Oklahoma, Norman, Oklahoma, Representing the American Physical Society.

The results of research in physics as a rule are published in special journals in the form of technical articles. It is difficult for the busy teacher to keep up with the progress of his science except through general articles and books. Unfortunately there are not many such books. It is the intention of this department to call special attention to those which come to its attention.

WITHIN THE ATOM.1

It is remarkable that John Mills, the author of Within the Atom, should have been able to compress into the compass of one small volume such a readable and complete summary of the discoveries of modern physics. To review this book by the method previously employed is impossible. Usually we have gleaned from a book the material for a short article hoping that the article itself would be of value and at the same time would give a correct impression of the character of the work. Within the Atom does this for the literature of modern physics and to attempt to re-distil such a splendid distillate would be entirely out of place. Consequently we shall attempt merely to give an idea of the nature of the work and suggest how it may prove of pleasure and value to teachers of physics.

The subtitle, "A Popular View of Electrons and Quanta," may easily be misinterpreted. Any layman who expects to find easy reading will be disappointed, but he need not feel deceived, for no more "popular" treatment could be found and remain sufficiently technical to be fair to the subject. Nor will the book be easy reading for the teacher of physics, for the more familiar he is with modern physics the more enjoyable and profitable will his reading be. The book will probably be more popular with teachers than the average reader.

The author shows very good judgment in abruptly plunging into the subject and introducing his audience to the electron and the proton on the first page. After personifying the two electrical elements sufficiently to overcome any feeling of strangeness on the part of the general reader he takes pains to emphasize the mechanistic side of this ultra microscopic world by using the terms tractate and pellate for the familiar attraction and repulsion of our text books.

Within the Atom, by John Mills. D. Van Nostrand Co., New York, 215 pp., illustrated, Price, $2.00.

In the first ten pages atomic number and radioactivity are touched upon and in the second and third chapters we find carefully laid out a physical basis for chemical action and the characteristics of the various elements. Finally the periodic table is given a vital meaning through an explanation so simple that any school boy, first wondering at the mysteries of chemistry as presented in the ordinary text book, would find many of them explained away.

The more familiar facts of radioactivity and conduction of electricity in gases are touched upon, followed by a most interesting chapter on conduction of electricity through solids and the simpler interactions and phenomena of electric and magnetic circuits. The writer of this review was particularly pleased with this chapter since he has found by experience that the introduction of the electron theory at the start in elementary courses makes the teaching of electrostatics and "current" electricity much easier for the students.

The chapter on the proof of the existence of the electron, including references to the early pioneer work of Thomson and the latter accurate determinations of Millikan, is followed by a chapter on the isolation of the proton or positive unit of electricity. Here is found a discussion of Wilson's photographs of the traces of beta and alpha particles, Thomson's positive ray analysis, Moseley's X-ray spectra, and Rutherford's bombardments of atomic nuclei.

To X-rays, crystal structure, and atomic numbers are devoted two chapters, after which the author plunges fearlessly into the quantum theory.

The appendix on the "Magnitudes of Electrons and Quanta" is a store of interesting data: The masses of hydrogen molecules, electrons and protons; the velocities of alpha and beta particles and quanta (or light); the energy of quanta, of gas molecules and electrons, etc. It is very useful to have such figures collected for ready reference.

In high school and college texts the electron and the new physics has been given a place in the regular reading matter and no longer is relegated to footnotes, small type or an appendix. However, the means by which the teacher who has not had the privileges of recent intensive study can keep adequately in touch with the rapid progress of physical science have not been good. While Within the Atom cannot take the place of special treatises it serves the desirable purpose of making a wealth of useful material available in a form especially adapted to the busy teacher.