The Mediterranean Sea 223 



salt is the outward under current in the Straits 1 . Hence the 

 inward upper current must be sufficient to replace the water 

 lost both by evaporation and by the outflow of the under 

 urrent. We may take the Atlantic water to contain 3-6 per 

 and the Mediterranean to contain 3*9 per cent, of salt. 

 In order that the under current may remove exactly as much 

 salt as is brought in by the upper one, their volumes must be 

 in the inverse ratio of their saline contents, or the volume of 

 the upper current must be to that of the under one in the 

 ratio 39 : 36 or 1000 : 923 ; so that only 7-7 per cent, of the 

 inflow goes to replace the water removed by evaporation, 

 while the remaining 92-3 per cent, replaces the water of the 

 under current. We have then for the total volume of the 

 inward current per annum: 



TOO 



v = v = 1170 x io 12 cubic feet. 



77 



The width of the Straits from Tarifa to Point Cires is eight 

 S or 48,000 feet, and the average depth of the stream may 



ly be taken as 100 fathoms; hence the sectional area is in 

 round numbers 29,000,000 square feet. 



Dividing the volume by the area, we have for the mean 

 annual flow: 



1170 x io 12 



R = g- = 40 x io 6 feet. 



29 x io 6 



R ducing this to miles per day, we find that if the above data 



are correct the inflowing current at the Straits of Gibraltar 



night to l>e equivalent to a current eight miles wide. 100 fathoms 



> and running with the uniform velocity of 18-3 miles in 



:tv-f>ur hours. As the currents are reversed with the 



tin- balance of inflow over outflow in the upper 



nt It i- worthy of remark that tin- flood tide runs to 



the westward at tin- surface ami the ebb to the eastward. The 



lollnwing table of tides at places inside and outride the StiaiN 



will show that the mere differences of level due to the different 



tid.il r, (i nt localities are Mittn imt to cause strong 



.ii current 



1 Sec Contents, p. x 



