1 5 inches at a speed of approximately 3 3 cycles per second the speed and distance of travel are selected so that the samples never experience negative gravitational loading and therefore never cavitate for a 0 75 inch spacing between the axis of drive wheel 61 and cam 63 the maximum speed of wheel 61 at which cavitation is avoided is 216 rpm this provides a maximum acceleration to the cuvettes of 32 ft sec 2 and a reciprocation rate of 3 6 cycles per second to provide synchronization signals for the demodulation circuitry utilized in conjunction with the spectroflourometer for demodulating the alternate time multiplexed sample measurements into a single differential output signal the sample positioning assembly 40 includes a pair of position transducers 80 and 81 which are actuated by an arm 82 carried on the cuvette carrier drive arm 60 these position transducers which may be conventional optical type transducers having their own light source for detecting the proximity of arm 82 are preferably adjustable along the axis of reciprocation to allow a close correspondence to be obtained between the cuvettes being in position and the presence of a synchronizing signal referring to fig8 the output of position detector 80 representing positioning of the lower cuvette 43.