This thesis is concerned with the development of a compact, sensitive and reliable instrument for determination of the polarization of fluorescence of f1uorescein tagged molecules in solution. The instrument as designed and constructed differs from others (2, 3, 4, 5, 6, 8, 9) . The difference is that all of its optical system is aligned on a single axis. This was accomplished by the use of an ellipsoidal mirror positioned between the excitation source and the phototube fluorescence signal

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... ver. In addition, the excitation source, a 45 watt tungsten-iodide light was electronically regulated to control the intensity. Two types of determinations were made to verify the perfonnance of the instrument. The first was the absolute sensitivity to varying fluorescein concentrations. Concentrations of fluorescein in 0.1 molar sodium phosphate buffer were prepared ranging from 10-6 molar to 10-11 molar. After the minimum detectable concentration was determined, five runs on samples of each concentration from the minimum detectable to 10-6 were made. The second check was for the sensitivity and linearity of the system in the measurement of polarization. Solutions of glycerol ranging from 62% to 90% were prepared with 10-6 molar fluorescein concentration. The data from the fluorescein sensitivity and polarization runs were averaged and the averages plotted on linear paper. In each case the instrument exhibited excellent linear response and reasonable standard deviation.