The amplification and distribution of speech and music by means of microphones, amplifiers and loud-speakers is one of the youngest of the electrical sciences. Only 20 years ago “Public Address,” the name by which the system is universally known, was regarded as only a scientific toy by the public. During the ensuing years, however, notable improvements have been made, and this paper traces the history and development of public address systems from their first appearance in this country to the present day.Although analogous to telephony and broadcasting, public address presents many widely divergent problems, particularly in the design and location of the various elements, which must vary for indoor or outdoor use, also for reinforcing the original sound or for use as a sound-diffusion system.A description of the various types of microphones, amplifiers and loud-speakers which have been used is given, and their advantages and disadvantages are considered in the light of present-day knowledge.The acoustic problems in auditoria are discussed, showing the need for co-operation between architect and acoustic engineer in their design, with suggestions for the planning of public address installations to overcome defects in the design of auditoria causing reflection and reverberation. It is also shown how these troubles can be overcome in outside broadcasts by the proper placing of subsidiary loud-speakers.The problems of “time delay” are discussed at length and proposals made so that the normal result of distance can be produced without an unwanted echo effect. Means are also given for artificially producing “time delay” when desired.Consideration is given to the intensity necessary to overcome the noises caused by the audience in confined spaces, and wind noise in the open air.Auditory perspective by “stereoscopic” means, which requires the highest possible fidelity of reproduction, is briefly described, and the paper concludes with descriptions of three installations as typical examples of the employment of the principles advocated.