74 Mr. S. Taylor on Colours shoivn by thin liquid [Jan. 31, 



operating in this manner with apertures of various shapes, I obtained 

 a large number of distinct figures : a few of the least complex have 

 been selected for illustration. 



In figs. 9, 10, 11, the aperture used was an equilateral triangle ; in 

 figs. 12, 13, 14, a square, The general character of these results will, 

 after the explanations already given, be readily understood on inspec- 

 tion of the diagrams. Their axis of symmetry depended on the position 

 of the film with reference to that of the tuning-fork. 



When larger apertures, or a fork and box of higher pitch, were 

 used, the resulting figures became rapidly more complex, and forms 

 were readily obtained in which the whole film was covered with an 

 uniform pattern consisting of some single figure analogous to one of 

 those already described repeated over and over again. With very 

 acute sounds the separate figures became too small for recognition and 

 too numerous for counting. 



The resonance of an air-cavity is, as is well known, not limited to 

 supporting a note of one single degree of pitch, but can also reinforce 

 other notes, provided they are not too far distant from its proper or 

 fundamental tone. It was therefore to be expected that colour-figures 

 could be obtained from a film in the mouth of a resonator by employ- 

 ing sounds other than that to which its cavity was tuned. In putting 

 this to the test of experiment I found it convenient to replace the 

 sounds of mounted tuning-forks by those of my own voice. The film, 

 formed as at first in the orifice of a resonator, showed itself sensitive 

 to very slight differences of pitch. When the note sung was some- 

 where in the neighbourhood of the resonator's proper tone, the 

 smallest sharpening or flattening which my voice could produce led 

 to an instantaneous and unmistakable change of figure. Moreover, 

 the limits of pitch on either side of the resonator's own note, within 

 which permanent figures could be obtained, were considerably wider 

 than those between which audible reinforcement by the resonator 

 itself occurred. 



In order to test the capacity of two figures corresponding to tones 

 of different pitch for coalescing into a regular resultant-form, I placed 

 a film symmetrically with respect to the open ends of two resonance- 

 boxes belonging to forks forming consonant intervals with each 

 other. By exciting either fork separately a steady figure was 

 obtained, but the coexistence of their sounds caused an immediate 

 tumultuous movement from which no permanent joint form emerged. 

 There seemed to be an absolute incompatibility between the two 

 figures which made all compromise impossible. Desirous of ascer- 

 taining whether this repugnance extended to the case of sounds all 

 but identical in pitch, I used a pair of unison forks, one of which had 

 been slightly flattened so as to beat about twice per second with its 

 fellow. Some very interesting phenomena were the result. The fixed 



