290 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



temperature, takes place, replacing the lower cold strata of the Baltic. 

 In the latter case the increase of temperature is combined with an in- 

 crease of specific gravity. This was observed at Kiel on the 16th of 

 August, 1871, when the specific gravity was 1.0118; temperature, 50° F.; 

 while on the 21st of the same month the specific gravity was 1.0140 ; 

 temperature, 56°. 75 F. These sudden variations are very singular, for 

 the reason that usually the changes in the depths are very slow and 

 gradual, and often for weeks are scarcely perceptible. Such simultaneous 

 changes of temperature and percentage of salt have been noticed at aU 

 observing stations along the Baltic. Thus, for instance, at Sonderbiu-g 

 it was observed that the temperature, which from the 13th of December, 

 1872, to the 22d of January, 1873, at 10 fathoms was lower than 41° F., 

 suddenly changed to 42<^.l F., while at the same time the specific grav- 

 ity of 1.0195 increased to 1.0243, owing to a powerful current of warmer and 

 heavier water from the German Ocean. If, on the one hand, the Baltic 

 in summer furnishes an excess of heat to the German Ocean by the upper 

 current, the latter in winter, on the other hand, by the under current 

 effects a rise of temperature in the former. This source of heat for the 

 winter is of especially good service in the western portion of the Baltic, 

 and is certainly an important climatic element. It is not yet established 

 with certainty how far to the east this under current extends. The 

 smaller the percentage of salt the greater the maximum of density ; hence 

 it is probable that, notwithstanding the lower temperature of the winter 

 in the north and east, the water in the greater depths never coeds to the 

 extent of that in the west. Experience, however, on this point is wanting. 

 Eegarding the relations of temperature in the German Ocean, but Yew 

 observations have thus far been made. Stations were not estabUshed 

 previous to 1872. The facts observed, however, are (1) the annual period 

 of the temperature of the water decreases towards the west; (2) the differ- 

 ence of temperature between the strata of different depths is smaller than 

 in the Baltic; and (3) a decrease to the freezing-point never occurs. 

 During the expeditions currents from different sources could easily be 

 traced by the thermometer and hydrometer; for instance, the currents 

 of the Elbe and Baltic. The following table from Mayer's work contains 

 some older observations on the average temperatures of the Baltic, 

 Kattegat, and Irish coast, which show very distinctly the decrease of the 

 differences in the annual periods : 



Month. 



January . . 

 February . 

 Mari'h .'. . 



April 



May 



June , 



July 



August.. . 

 September 

 October . . 

 Xovember 

 December 



Baltic. Kattegat. Irish coast, 



35.8 

 36.3 

 30. 9 

 44.6 

 52.7 

 59.0 

 64.6 

 64.8 

 59.9 

 53.4 

 44.6 

 39.9 



36.3 

 42.6 

 49.5 

 54.7 

 60.8 

 62.1 

 57.8 

 52.0 

 42.8 



46.0 

 45.7 

 45.9 

 48.4 

 51.8 

 55.4 

 58.7 

 60.1 

 59.4 

 55.2 

 49.1 

 48.2 



