1: PROCEEDINGS OF THE NATIONAL. MUSEUM vol.80 



salinity between the surface and the bottom, even where the water 

 IS very shallow. In water from 15 to 20 meters deep it is not at 

 all unusual to find the salinity at the bottom from two to two and a 

 half times as great as at the surface. At Station U (fig. 1), oppo- 

 site the mouth of the Patapsco River, where the water is only 11 

 meters deep, the salinity at the bottom is occasionally four times that 

 at the surface. 



Temperature. — In temperature just the reverse is true: There is 

 m equalization instead of a differentiation. On August 21, 1920, 

 the difference in temperature between the surface water and the 

 bottom water of the outside ocean at a depth of 20 fathoms was 

 more than 16° C. At the deepest station (G) in the mouth of the 

 bay on the following day the difference was 11.5°, but at Station B, 

 20 miles up the bay, it was only 2^^°. At practically every station 

 tn the bay except the three at the very mouth the difference between 

 fche surface and bottom temperatures was less than 2° and often 

 less than 1°. Even at Station R, where the water was 47.5 meters 

 deep, considerably more than 20 fathoms, there was a difference of 

 Jess than 1^°. But at the same time large areas of very shallow 

 water along shore may be heated during summer to a comparatively 

 high temperature compared with the deeper water. 



Also, during spring the quantity of fresh water poured into the 

 bay is greatly increased, while during the late summer and early 

 fall it is considerably diminished. Hence the resultant combinations 

 vary greatly with the seasons. The changes produced by all this 

 intermingling of tide and seasons, temperature and salinity are 

 iimch the same as those in the old-fashioned kaleidoscope. Each 

 (!ombination is different from all the others, and there are never 

 any exact repetitions. 



NErrS EMPLOYKD 



In collecting the material four kinds of nets were used, called, 

 respectively, " stramin net " and Nos. 6, 18, and 20. The stramin net 

 liad the coarsest and No. 20 the finest mesh. Each net was usuallv 

 rowed for 10 minutes and then emptied. Sometimes two or three 

 nets of different mesh were towed successively at the same station 

 with contrasting results. The vertical net was a large tow net of 

 medium mesh, lowered to the bottom and then immediately drawn 

 to the surface. Its contents, of course, included material from every 

 stratum of depth, with no possibility of determining the level from 

 <vhich any given specimen was obtained. The bottom net was one 

 of medium mesh, fastened to a beam trawl frame and towed along 

 f^he bottom for 10 minutes. Most of its contents would be bottom 

 material, but as the net was nonclosing copepods could get into 

 it while it was being lowered and raised. 



