It is unnecessary perhaps at the outset to dwell on the nature of tone quality or timbre. Most musicians nowadays are aware that this elusive characteristic has given up its secret and that what the scientist calls the ‘note’ of a musical instrument can be split up into a number of simple ‘tones’ and that it is the relative number and magnitude of these components that determines timbre; tells us, for example, why a violin and a clarinet or even two violins do not when played severally sound the same when producing a note at the same fundamental pitch. In many cases these component tones are members of the harmonic series, i.e., their frequencies bear simple ratios to the fundamental or component of lowest pitch, but again often other tones—not harmonics—intrude, whose origin is to be traced to the vibrations of the invariant parts of the instrument such as the belly of the violin or the metal tube of the trumpet and which do not alter much when the player passes from one note to another. By means of the apparatus I am about to describe this characteristic ‘formant’ of an instrument can be delineated after precise analysis of the tone quality over the whole range of performance of the instrument. A knowledge of this factor is most important to the instrument maker. By persistent analysis of this type one can, for instance, reduce the difference between a Stradivarius and a Heath Robinson—pardon the mark!—to scientific terminology and then with the co-operation of the maker take steps to improve on a specimen of poor quality, checking the extent of one's improvements as one progresses. Work of this nature on stringed instruments has been carried out by Backhaus in Germany and Saunders in the United States. At Newcastle we have been mainly concerned with organ pipes and hope to deal with the wood-wind next.