The apparatus 75, wherein said 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 {HEAD ~ electrical signals representative} of the energy of the acoustic disturbances induced within {TAIL ~ the gas sample} by the first and second laser beams 
The apparatus 75 , wherein said 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 { HEAD ~ electrical signals representative } of the energy of the acoustic disturbances induced within { TAIL ~ the gas sample } by the first and second laser beams
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH