600 CYCLES OF ORGANIC AND INORGANIC SUBSTANCES 



out evidently discordant temperatures from a set and to reject 

 them. In 1958 the agreement between paired unprotected ther- 

 mometers was much better than expected. Paired unprotected ther- 

 mometers agreed well. Rogue readings were scarce. The discre- 

 pancies are no more than we should get by assuming that ther mo- 

 metric error in a depth measurement is no greater for unprotected 

 than for protected thermometers and that the error in depth 

 measurement is the statistical sum of error for the two types of 

 thermometer and for the pressure coefficient. 



We cannot account for the anomalies in depth in earlier years 

 as due to malfunctioning of unprotected thermometers. The ap- 

 parent discrepancies in depth measurement ha\'e proved to be 

 due to "vertical yawing." Research ships may resemble R.R.S. 

 Discovery II from which it is possible to maintain a nearly vertical 

 wire angle e\'en in a moderate gale or our own vessel Sarsia from 

 which it is not. 



Vertical Yawing 



Our troubles seemed to be confined to occasions when Sarsia had 

 to work in strong gusty winds. When our wire has been near verti- 

 cal we have had no trouble. However, when the hydrographic wire 

 enters the surface of the sea at a considerable angle (Fig. 1), the 

 thrust of the water on the wire and the mass of the wire, the bottles 

 and the sinker attached to the wire result in a curved wire. The 

 bottom part of the wire will be much more nearly vertical than 

 the top part. To simplify the argument, it will be assumed that 

 the bottom part of the wire is indeed vertical. 



A gust of stronger wind will cause the speed of drift to increase. 

 At the surface, the wire angle will increase and at all depths at 

 which the wire is curved there will be a force normal to the wire 

 tending to prevent the wire straightening out. From this force a 

 vertical component may be resolved which tends to lift the wire, 

 and everything carried by it, through the water. The depth of 

 the hoist of bottles will become less. Now let the gust die away. 

 The only force acting on the bottles will be that of gravity, tending 

 to restore the wire to the vertical. The hoist of bottles will then 



