XXXIII. On the objective reality of combination tones

A. W. Rücker, E. Edser
1895 The London Edinburgh and Dublin Philosophical Magazine and Journal of Science  
the amplitudes of the vibrations of the notes which give rise to them are so great that powers higher than the first have to be considered. He supported this view by mathematical demonstrations, and stated (' Sensations of Tone,' transl, by A. Ellis~ p. 157) that he had proved their objective existence by making membranes and resonators to respond to combinational tones produced by the siren and harmonium. These views and statements have been adversely criticised by K~inig, Bosanquet, and
more » ... osanquet, and Preyer. A very lucid account of the controversy was given by the late Mr. Ellis in his translation of the Tonem_p.findungen, and the net result of the impression produced in his mind is shown by two notes on pages 156 and 157. He there states that the result of Mr. Bosanquet's and Prof. Preyer's experiments is to show that the combinational tones are produced in the ear itself~ and that it is probable that the apparent reinforcement of the resonators noticed by ttelmholtz arose from imperfect blocking of both ears when using them. These statements were unqualified, and no condition was made as to the way in which the combination-tones were produced. Helmholtz, for reasons which we need not recount, regarded the siren as the best instrument for producing objective combination-tones ; and we recently determined to submit the question of their existence, which seemed to be decided against him, to another experimental test. In this paper we give the result of our investigations, as far as they have at present been carried out. We do not regard them as complete, but they at all events prove that when the conditions under which we experimented are fulfilled~ there can be no doubt that difference and summation-tones are produced which are capable of disturbing resonating bodies. The resonator employed in the first instance was a tuningfork. It is well known that this instrument is relatively difficult to excite by resonanc% and it was therefore necessary to use an extremely delicate method of detecting whether it was set in motion. For this purpose a mirror attached to one of the prongs was made one of a system by which Michelson's interference-bands were produced. A movement of the prong.amounting to half. a wave-length of light (say 1/80,000 of an mch) would alter the length of the path of one of the interfering rays by a wave-length. A periodic vibration of this amplitude would cause the band to disappear. It is therefore evident that an extremely minute movement could be detected. It was at first open to question whether the apparatus would not be so sensitive to accidental dis-Downloaded by [University of California Santa Barbara]
doi:10.1080/14786449508620728 fatcat:jico3tkiqzcn3lsba3ox4wskim