The subject of noise and its measurement, dealt with by Dr. G. W. C. Kaye in his recent Royal Institution discourse, which forms our supplement this week, is one of great practical importance and wide interest. It is becoming increasingly apparent that excessive or particularly irritating noise is injurious to health, happiness, and working efficiency. Laboratory measurements have shown that even during sleep sufficiently deep to render the sleeper unconscious of any sounds, response to such sounds as are made by the early morning milkman is readily detectible. There are numerous practical difficulties in the quantitative measurement of noise, since acoustical, psychological, and physiological factors are all concerned. A general survey of the methods at present in use is given by Dr. Kaye. The results gathered from several independent sources deal with all types of noises, from the whispering human voice, the crying of twins, and the applause at Lindbergh's reception in New York, to transport noises, the roaring of lions, and the sounds of Niagara Falls.