284 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



the work to a Commission stationed in Kiel. This Commission took 

 into consideration the following points, ^iz : 



(«) Depth, height of the water, condition of the bottom, quantity of 

 salt and air of the water, and temperature. 



(&) Flora and fauna of the sea. 



(c) Distribution, propagation, and migration of the useful animals — 

 problems which requked for their proper discussion and settlement ob- 

 servations at numerous stations along the coast, as well as on the high 

 sea. From the preliminary observations of Mayer it was known that in 

 the western part of the Baltic the variations in the water are analogous 

 to those of the climate ; further, it was established as a fact that the 

 physical conditions of the eastern and western portions differed — for in- 

 stance, the variations in the amount of salt show smaller differences in 

 the eastern than in the western part. This is in anotlier relation also 

 found in the German Ocean. The work was commenced by establishing 

 a number of stations along the German as well as the foreign coast, one 

 station being at Heligoland. Two expeditions have thus far been sent 

 out, one in 1871, another in 1872, the former to the Baltic, the latter to 

 the German Ocean. The following is a brief summary of the work of 

 the Commission, the mode of observation, and the results, with the ex- 

 ception of the part relating to organisms, for which the reader is referred 

 to the publications of the Commission. 



The most important points for determination were the a7nonnt of salt 

 and the temperature. As variations in these depend upon the currents, 

 and these again upon various causes, as the height of the water, the 

 direction and velocity of the wind, the duration of ice -formation, the 

 amount of rain and snow in the drift regions, &c., it was evident that a 

 thorough study would requke a long series of observations. The amount 

 of air contained in the water could not be well determined on account of 

 the want of methods sufficiently simple for the several stations. The 

 proportion of salt is important for several reasons : 



First. The difference in the amount of the saline substance is one 

 cause of the currents, the heavier salt water having the tendency to flow 

 to the deepest place. In this manner two cui-rents may be produced — a 

 vertical one when from some cause or other the upper strata become 

 more concentrated, and a horizontal one when two strata of different 

 densities lie side by side. The latter currents predominate in the Ger- 

 man Ocean as well as in the Baltic Sea. 



Second. The strata in motion will also have temperature of their own. 

 For the waters in question this can be easily shown. The under current 

 of the heavier water of the German Ocean can readily be recognized by 

 its temperature upon its entrance in the Baltic, and the same is the case 

 with the light ujiper current issuing from the Baltic. 



An analogous difference is found in comparing the different strata of 

 the German Ocean with the waters of the Atlantic. Furthermore, there 

 is a certain relation between the amount of salt and carbonic acid con- 



