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. 21 . unique design of the suspension chamber provided the necessary stability to allow the crystal to be suspended for periods much longer than have been previously achieved. The arrangement of the shelves in the fog chamber helped to ensure that the air would become sufficiently homogeneous with respect to temperature and droplet concentration. The honeycomb, which was made replaceable in case of ice buildup, suppressed turbulence and created a laminar flow. The design of the suction system evenly applied the vacuum force and allowed quick changes of the flow without adjusting the power of the vacuum cleaner. The redesigned pressure cooker produced steam at a constant rate so that the liquid water content remained unchanged during the entire growth period. These and other features eliminated technical problems that prevented long growth periods under controlled conditions, and made the simulation of the natural condition better. However, a few drawbacks persisted that may have affected the usefulness of this study. The pitot tube assembly consistently indicated fall velocities about 20 to 40 percent higher than values obtained by later investigators. This inconsistency, which will be shown later, is probably due to the enhanced flow in the tube above the suspension chamber, which has more cross sectional area. The plaster of paris method probably does not reliably give the liquid water content of the supercooled fog. The difficulty in accurately measuring the mass increase by water accumulation in the much more massive U-shape tube and the possibility of ice formation in the tube created some uncertainty for this method. Complex ice crystal shapes presented difficulties in providing a consistent determination of the dimension at low temperatures. Similarly, thin plates made the . . . . . . . . .