226 Lord Rayleigh on our 



transition in respect of right and left effect occurs at this 

 moment, and the sequence rule already stated defining whether 

 the transition is from right to left or from left to right is found 

 to be obeyed. 



There are some advantages, of course, in an experimental 

 arrangement allowing the sounds to be uniformly maintained. 

 As in Helmholtz's vowel investigations, the 256 forks can be 

 driven by the 128 interrupter-forks already employed, ;md in 

 each case the frequency of the driven fork is the exact double 

 of the frequency of the driving fork. The observations may 

 be made in two ways. Either the 256 forks may themselves 

 be brought close to the ears, leading wires being conveyed 

 through the wall ; or, what is on the whole preferable, the 

 method employed for the 128 per second tones may be 

 followed. In this case each 256 fork is associated with two 

 resonators, vibrating in opposite phases, with one of which 

 the pipe leading to the observation room is connected. The 

 isolation was good, each sound being inaudible through the 

 tube provided for the other. 



Excellent results were obtained in this way. With good 

 adjustment the transitions between right and left were sharply 

 marked and the sequence rule already formulated was obeyed. 

 It is again to be noted that right and left effects are observable 

 in the neighbourhood of phase-opposition, a situation which 



