182 BELL SYSTEM TECHNICAL JOURNAL 



ginecring theory, an infinite series of complementary waves exist. It 

 is through these waves that the phenomena of radiation are directly 

 accounted for. E.xcept for the phenomena of radiation, however, the 

 complementary waves are of theoretical rather than practical interest 

 in present-day transmission practice, and except in extreme cases they 

 may be ignored in practice without appreciable error. 



Sound Magnification and Its Application to the Requirements of the 

 Deafened.^- Harvkv Fletcher. A general description of the gen- 

 eration and projiagation of sound waves was given and experiments 

 performed to illustrate the principles involved. The general require- 

 ments for aiding persons ha\ing various amounts of deafness were 

 outlined. The relation between the loudness of speech received by 

 the ear in a room of average acoustic characteristics and the distance 

 the speaker is away from the ear was illustrated by a chart. Also, 

 a chart showing the characteristic frequency regions and loudness 

 levels of the fundamental speech sounds, and one showing the interpre- 

 tation of speech at various loudness levels by persons having various 

 degrees of hearing, were exhibited. By means of these three charts 

 it was shown how one could predict the amount of intelligibility which 

 would be obtained by a person having a definitely measured amount 

 of hearing. In particular it was pointed out that such sounds as 

 th,f, and v will be the first sounds to be lost as the hearing decreases. 

 These sounds are the easiest ones to detect by lip reading so that 

 hearing aids and lip reading go hand in hand in aiding one wlio is 

 hard of hearing to obtain the proper interpretation. 



Abstract of a Telephone Transmission Reference SyslemP L. J. 

 SiviAN. The subject is dealt with in four parts: A — The function of 

 a transmission reference system; B — Requirements to be met by the 

 reference system; C — Work done on the construction and calibration 

 of a preliminary model of the new reference system; D — Proposed 

 future development of the new reference system in its final form to 

 be adopted as the standard for the Bell System. 



A brief discussion of the methods and apparatus entering into the 

 general problem of rating telephone transmission is given. It is 



" Lecture given before the .\nnii;il Conference of the .American Federation of 

 Organiziitions for the Hard of Hearing, Washington, U. C, Thursday, June S, and 

 published in Volta Review, Septenilwr, 1924. 



A large number of the audience who listened to this lecture were hard of hearing. 

 A rough measurement of the amount of hearing of each of those present was made 

 and groups arranged according to the degree of hearing. The amplification was 

 then adjusted to each group to suit their i)articular needs. The results seemed 

 to bo most gratifying, as nearly everybody said that it was the first time they ever 

 heard a public lecture of this sort without difficulty since they had become hard of 

 hearing. 



" Klcctrical Communications, Vol. Ill, pp. 114-126, 1924. 



