. The Earth beneath the sea : History . 20 Time (min) Fig. 2. Variation with time of the temperature difference between the top and the bottom of a probe cm in diameter. The full-line curve represents the theoretical ex- pression (1). (After Bullard et al., 1956, fig. 2.) in the probe used in Discovery II it would raise its temperature by °C, which is considerably larger than the temi^erature difference to be measured. In practice part of the heat goes into the sediment. The time taken for heat to spread from the surface of the probe to the centre is only a few minutes and is much short
. The Earth beneath the sea : History . 20 Time (min) Fig. 2. Variation with time of the temperature difference between the top and the bottom of a probe cm in diameter. The full-line curve represents the theoretical ex- pression (1). (After Bullard et al., 1956, fig. 2.) in the probe used in Discovery II it would raise its temperature by °C, which is considerably larger than the temi^erature difference to be measured. In practice part of the heat goes into the sediment. The time taken for heat to spread from the surface of the probe to the centre is only a few minutes and is much shorter than the time needed for the probe to reach temperature equilibrium with the sediment. If the lower end of the probe is heated above the temperature of the sediment into which it has penetrated the temperature will rise for about 3 min, pass through a maximum and then fall towards its final value as shown in Fig. 2. It is not practicable to leave a probe in the bottom for more than about 40 min; after this time the temperature gradient in the probe usually exceeds that in the sediment by 10 to 15%. It is, therefore, desirable to extrapolate the observed temperature differences to get the value which would be obtained after a very long time. In making this correction it may be assumed that any cross-section of the probe is at a uniform temperature and that conduction is
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Keywords: ., bookcentury1900, bookcollectionbiodivers, booksubjectoceanbottom
