yields very definite information concerning the parities of the nuclear levels involved. The ambiguities left in the examples discussed in this paper arise from a paucity of theoretical predictions for higher multipole transitions, to the possibility of interference for mixed radiation, and to the preliminary character of the angular correlation data. If these obstacles are eliminated the experiments with the polarimeter have only to decide the existence or non-existence of a polarization in the * The angular correlation of successive gamma-rays emitted by six even-even nuclei has been investigated and found to be anisotropic in every case, and of the magnitude expected theoretically. Effects of external magnetic fields and of chemical binding on the correlations are found to be smaller than the experimental uncertainty for some exploratory experiments. Interpretation of the results in terms of the nuclear states involved is in general possible by use of additional evidence such as relative transition probabilities. ANGULAR CORRELATIONOF GAMMA-RAYS

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Without gelatin, the product iT1/2 is about ten times greater than the theoretical value which could be expected in the absence of any convection. The addition of 1 milligram per liter of gelatin reduces this product to about half of its original too high value. With 20 to 40 mg. per liter, the non-steady state We wish to express our gratitude to Dr. Joseph J. Donovan of Houdry Process Corporation, to Dr. Erwin Sterling of Carnegie Institute of Technology and to Dr. Paul Delahay of Louisiana State University for their courteous criticism and suggestions concerning the present paper.Acknowledgment with gratitude is also expressed to the Belgian National Scientific Research Foundation which granted a fellowship to one of the authors during part of the time devoted to this research.CHEMICAL NATURE OF SILICA CARRIED ß STEAM .

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