@ 150-pound weight was attached to the bathythermograph (BT) to insure vertical descent 80 as to obtain reliable estimates of the depth of the thermocline. Four destroyers took additional bathythermograph readings. The resulting bathythermograms were used for additional knowledge of thermocline depth in the area. Usually, oceanographers attach to each water sampling tank (Nansen bottle) a pair of precision thermometersof peculiar design, that permits them to measure and to retain a record of that temperature which existed at the moment they were turned upside down. This upsetting or “reversing” is accomplished in situ by sliding weights or “messengers’ 3 down the cable so as to strike releasing triggers. Oneof these pair is “protected” from the hydrostatic water pressure by a thick glass shell; it therefore records only the sea temperature. The other thermometer is “unprotected,” that is, its bulb is exposed to the squeeze of the sea pressure and therefore the deviation of its reading from that of the protected thermometer records the in situ pressure and hence the depth. Tempera- tures can be read to “499 degree centigrade, and depths to one meteror to about 4) per- cent at 1,000 metérs depth by this traditional oceanographic procedure. Precise and well calibrated reversing thermometers took temperatures at each Nansen sampling point. Because there were no unprotected reversing thermometers available, no thermometric depth measurements could be made; so the depth of each water sample had to be computed by intercomparison with the bathythermograph measurements. Few very-deep casts were made because of this lack of unprotected reversing thermometers such as are normally relied upon for measuring depths in hydrographic operations. 2.4 PLANKTON SAMPLING Samples of zooplankton were recovered at two stations when a standard one-meterdiameter silk plankton net was lowered through the upper mixed water. One haul was made at night and the other in daylight. These samples were forwarded to SIO for activity analysis and examination of organisms. Some evidence of selective concentration was presented. These findings are presented in a separate paper. It was evident—-even from simple gamma measurements made on deck-—that zoo- plankton concentrate gammaactivity of several orders of magnitude. Plankton taken Rew from a water mass, whose activity is difficult to detect with crude instruments, appear very radioactive when the detector is brought near the sample bottle holding them. 25