944 



SCIENGE. 



[N. S. Vol. VIII. No. 209, 



Ocean in the tropics along the meridian of 

 151° 45' W., a short distance to the east- 

 ward of the Hawaiian Islands. The sur- 

 face densities in this section, and generally 

 in the South Pacific, are higher than in the 

 ISTorth Pacific; this is due mainly to the 

 fact that no large rivers, draining extensive 

 continental areas, empty their waters into 

 the South Pacific. As a rule the densities 

 decrease from the surface to the depth of 

 about 300 fathoms, where densities from 

 1..0254 to 1.0257 are found; thence there 

 is a very gradual increase to the bottom, 

 where 1.0259 is reached. This depth of 

 300 fathoms indicates the approximate limit 

 to which salt and heat are carried through 

 the process of surface evaporation. But 

 there is another cause which brings the 

 waters of the ocean into motion and tends 

 to diffuse salt and heat into regions which 

 are not affected directly by evaporation. 

 If two differently constituted bodies of sea- 

 water meet under the conditions of equilib- 

 rium, the one composed of dense and warm, 

 the other of light and cold water, an efifort 

 towards equalization of the proportions of 

 salt and heat at the plane of contact will 

 develop a tendency in the denser water to 

 sink and in the lighter water to rise to a 

 higher level. The waters of the South 

 Pacific, being denser and warmer in the 

 upper stratum than those of the north Pa- 

 cific, exhibit this tendency to sink in the 

 vicinity of the equator, where with a den- 

 sity of 1.0259 to 1.0260 at a depth of 200 

 fathoms they descend to more than 1,000 

 fathoms' depth. At the same time the light 

 water of the north Pacific rises from the 

 depth of 800 fathoms in latitude 20° N. 

 with a density of 1.0254 in an oblique di- 

 rection towards the equator, arriving in 

 latitude 3° N. with a density of 1.0258 at 

 50 fathoms from the surface. The effects 

 of the sinking of the dense and the rising 

 of the cold water are shown in the diagram 

 of temperatures by the high temperatures 



between the equator and 10° IST. latitude at 

 all depths exceeding 150 fathoms and by 

 the existence of a minimum of surface tem- 

 perature at the equator itself. We note a 

 second example of bodies of water changiug- 

 their level in the upper left-hand part of 

 the diagram, where dense and warm water 

 from the region of the equatorial counter 

 current undermines the north equatorial 

 current and forces its light and cold water 

 towards the surface. The diagram has the 

 defect of showing motion in only two direc- 

 tions, vertical and meridional, while the 

 third component, the most important one, 

 that in an east-and-west direction is not 

 represented and hitherto has not received 

 our attention. The presence in the south 

 Pacific of water at the depth of 100 fathoms 

 with greater density than is found at the 

 surface cannot be accounted for by mere 

 sinking ' in loco,' but we have to assume 

 that the surface water has drifted to its 

 present position by a current from the east- 

 ward, while the lower water comes from a 

 more southerly direction. Likewise, we 

 find in latitude 9° 28' N. the density of 

 the surface water is 1.0250, and is nowhere 

 less than 1.0256 under the surface ; as we 

 cannot admit that in a region where density 

 decreases with depth water rising to the 

 surface should have its density reduced, we 

 must assume that the lightness of the sur- 

 face water is either due to precipitation or 

 to a curi'ent of light water, the north equa- 

 torial, and that the water of the density of 

 1.0256 may not reach the surface, or, if at 

 all, then probably far to the westward of 

 the position indicated on the diagram. 



A. LiNDENKOHL. 



THE STORING OF PAMPHLETS. 

 The question of the best method of keep- 

 ing pamphlets in a private library has be- 

 come a question of great practical impor- 

 tance to the scientific worker. Owing to 

 the custom of exchanging reprints of arti- 



