ioo On Similarities in the 



there was a difference, and at 30 fathoms the water was running 

 so strongly to the south-east that it was impossible to make 

 observations of temperature, as the lines, heavily loaded, 

 drifted straight out, and could not be sunk by any weight 

 the strain of which they could bear. 



In the Pacific the counter equatorial current in the open 

 ocean was well observed by the "Challenger" on her voyage 

 from Hawaii to Tahiti. Her observations are represented in 

 Diagrams C and D. The former gives the surface current in miles 

 per day along a mean meridian of 150 W., easterly current 

 being laid off above, and westerly current below, the meridian 

 line, along which degrees of latitude are measured. The latter 

 represents the distribution of true density, that is, the density 

 of the water due to its salinity and temperature combined, but 

 at constant pressure, in the water from the surface to a depth 

 of 200 fathoms. As these lines of equal density coincide 

 nearly with corresponding isothermal lines, the approximately 

 corresponding isothermals are indicated in the diagrams. 

 The thick lines intruding unconformably into the diagram 

 represent density at constant temperature (60 F.), which is 

 proportional to salinity. The horizontal scale of degrees of 

 latitude is the same for both diagrams. The current diagram 

 is carried to lat. 7 S., while the density diagram stops at 

 3 48' S. The easterly current was found between the parallels 

 of 5 and 10 N., there being two streaks of maximum velocity, 

 one between 7 and 8 N., and the other between 9 and 10. 

 In the former the mean daily set was 54 miles ; in the latter 

 it was probably quite as high, but it could not be accurately 

 determined, as the ship passed from westerly to easterly 

 current in the course of the 24 hours, and the observed current 

 of 20 miles represented the difference of the two. The streaks 

 or axes of strong easterly current are sharply denned by areas 

 of abnormally low surface density. The whole of the area 

 of easterly running water has a comparatively low density, 

 but where there is a sudden acceleration of its velocity there 

 is a correspondingly sudden drop in its density, so that the 

 existence of a strong easterly current in equatorial regions 

 may be guessed with great probability by the use of the hydro- 



