354 MISCELLANEOUS STUDIES 



problem agree well with those in nature. The application of theory 

 to practical problems is rendered especially difficult, first, because of 

 lack of knowledge of the frictional resistance to the motion of sea 

 water, and, second, because of the uncertainty regarding the current 

 produced by a wind of given velocity and direction. 



One of the most important needs now is a comprehensive pro- 

 gramme of observations at sea, of the currents themselves and their 

 causes, supplemented by attempts to formulate hydrodynamical prob- 

 lems whose solution shall be consistent with the observations. .Much 

 credit is due to the pioneer investigators, Zoppritz, Mohn, Bjerknes, 

 Sandstrom, Ekman, Jacobsen, and others, for their development of 

 methods of dealing with such problems. 



Another important aid to the determination of oceanic circulation 

 is found in the fact that a current consists of water particles tending 

 to preserve their temperature and salinity as they move along. Tln-s.- 

 characters change slowly and thus serve to depict the currents some- 

 what as do floating objects that are readily identified. 



This part of the paper presents an attempt to develop, along the 

 line suggested in the following translation from Krummel (1911, 

 p. 439), a method of deducing currents from the temperature dis- 

 tribution : 



No simple rule has been formulated for determining currents from tempera- 

 ture charts. But it is conceivable if not certain that a systematic investigation 

 of the so-called individual temperature changes will give a reliable basis for 

 the estimation of currents from temperatures. (We must distinguish between 

 the annual temperature range, corresponding to definite geographical positions, 

 and the practically uninvestigated temperature changes which one and the same 

 water particle undergoes along the great horizontal current systems. In a 

 continuous current, for example, the Gulf Stream, these individual temperature 

 changes which must be distinguished from changes at a given position may 

 run through the whole range from tropical heat to the freezing point.) The 

 problem is, however, very difficult, and a cursory comparison of the current 

 charts in the Atlantic as prepared from the Log Book of the "Seewarte" 

 reveals the great complexity of these closely inter-related phenomena. In 

 general, in connection with all water motions time is an all important factor. 

 Rapid and slow currents behave very differently as regards their heat content, 

 and can therefore give rise to widely different types of isotherms. Xo constant 

 angle between stream lines and isotherms can be proposed; the angle can vary 

 between and 90. The most frequent case is that of stream lines cutting 

 the isotherms obliquely. 



In general, the rate of change of heat in an element of volume can 

 be expressed by adding to the right-hand member of the differential 

 equation (3) the rate of change due to other factors not considered on 



