INVESTIGATION OF BALTIC SEA AND GERMAN OCEAN. 287 



temperature of the Baltic by tlie entering under-currents. The tem- 

 perature of the Baltic varies greatly vnth. the respective temperature of 

 the air, the changes decreasing, of course, with the depth. The unequal 

 temperatures of increasing latitudes will be equalized by the perpetual 

 motions of the waters. 



The German Ocean shows much smaller variations of temperatures, 

 and undoubtedly will present different conditions at different points, 

 being connected with the Atlantic in the North by a wide and in the 

 South by a narrow channel, and again by a narrow channel with the 

 Baltic in the East. 



While throughout the year currents of but little variations enter 

 the channels from the Atlantic, those from the Baltic are of various 

 temperatures. This, together with the greater depth of the German 

 Ocean, will suffice to show that it requires years of observation and 

 prolonged study to determine the exact relations of temperature. The 

 observations hitherto made for different strata can only be considered 

 as initiating a closer study, the former investigations relating mainly 

 to surface-temperatures. The observations along the coast not having 

 to be made in great depths, the thermometer of the Commission could 

 be of a simple construction. The thermometer for ascertaining the sur- 

 face-temperature was very simple, reading to .2 of a degree ; the tem- 

 perature could be read either directlj^ in the ocean or in a large quantity 

 of water freshly drawn. For the observations of the temperature in 

 deep water the thermometers were surrounded by a thick layer of India 

 rubber, a poor conductor of heat. The instruments were compared, and 

 the time necessary for each to indicate a change in temperature was 

 noted, as well as that during which they marked the temperature of the 

 water after being exposed to the air. An hour was ascertained to be the 

 average time for each instrument to indicate the temperature of the 

 depth, and fully five minutes that between the removal of the instru- 

 ment from the water and any perceptible change. The thermometers 

 always remained at the desired depth for one hour before the tempera- 

 ture was read.* During the expeditions ui:)on the open sea this instru- 

 ment could be used only when the ship or boat lay still or was anchored ; 

 in all otlier cases Casella's maximum and minimum thermometer was 

 used. The results gained are the following : 



The temperature of the surface-water of the Baltic, and with dimin- 

 ished extremes also that of the depths, varies with the temperature of 

 the atmosphere. As an example the observations at two stations, Son- 

 derbiu'g and Kiel, are here given : 



'These thermometers, surroimded by ludia rubber, cau be had at Steger's iu Kiel. 



