On the genekal Causes of the Ocean-Currents. 



43 



its dilatatiuu through heat will already be tolerably rapid at a tempera- 

 ture as low as + 4° Ceut., and that the dilatation, though it really in- 

 creases at higher temperatures, do'fes not increase so rapidly as at lower. 

 The following little table, which indicates the ir.crease in volume, which 

 100,000 volumes of sea-water acquire for an increase of 1" Cent, of heat, 

 and beside which I have, for the sake of comparison, placed the corres- 

 ponding ciphers for pure water, will make this evident '). 



We see here that the dilatation of sea-water at the temperatures, 

 which take place in the superficial strata of the warmer seas, is not so 

 much greater than that of pure water, although at low temperatures, which 

 even there may be met with deep under the surface, it can be 10 

 times more rapid. Evaporation 0]i the other hand at low temperatures 

 is small, l)ut increases very rapidly with increased temperature. The in- 

 fluence of the sea-salt in liindering evaporation is more sensible at low 

 than at high temperatures, although that influence of S'/^ p. c. salt is 

 in general very trifling. 



Let us suppose the whole ocean to have had a temperature of 

 for example + 4° Cent., and that the unequal distribution of the solar 

 heat were just beginning to influence the surface. As the evaporation 

 of the water would at such a temperature be slow, whereas its dilata- 

 tion would already be tolerably rapid, the first effect of the heat ought 

 chiefly to be a surface-current from the equator towards the poles, follo- 

 wed by an under-circulation in the opposite direction, as I have shown 

 in explaining the streams produced by heat. This under-circulation will 



') The base, on which the calculation is made, is, lor pure water Mall-STRom's 

 tables and for the salt-water the tables in iny work: »Om Hafsvattuet vid Boliusliin- 

 ska kusten», Kongl. Sv. Vet.-Akad:s Handlingar 1870. 1 have there among other 

 things given complete tables of the volume of sea-water from — 5" Cent., determined 

 with the dilatomcter and calculated by the Method of least squares, for saltness of 2, 

 2',,, 3 and o'/o per cent. 



