{HEAD ~ The apparatus} 75, wherein said {TAIL ~ first acoustic wave} detecting means includes a pressure transducer disposed in acoustic disturbance receiving communication with each of said first and second photoacoustic cells to produce electrical signals representative of the energy of the acoustic disturbances induced within the gas sample by the first and second laser beams 
wherein
{ HEAD ~ The apparatus } 75 , wherein said { TAIL ~ first acoustic wave } detecting means includes a pressure transducer disposed in acoustic disturbance receiving communication with each of said first and second photoacoustic cells to produce electrical signals representative of the energy of the acoustic disturbances induced within the gas sample by the first and second laser beams
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