PHYSICAL OCEANOGRAPHY 301 



Figs. 206 and 207 show some of his results. At that time (in 

 the nineties) no systematic investigations of the Norwegian Sea 

 through any length of time had been carried on, so he could 

 only study the surface-temperatures noted at three Norwegian 

 lighthouses. 



In Fig. 206 we see the variations in the surface-temperature 

 off the west coast of Norway (indicated by the thick line) and 

 in the air-temperature at Orebro in Sweden (indicated by the 

 thin line), both for January during the years 1874 to 1892. The 

 vertical scale indicates the deviation from the mean temperature, 

 which for the coast-water is 5.3° C. and for the air 3.4" C. 

 On the whole the curves agree well, a high temperature in the 



74 7S 76 77 76 yjj 80 01 az ,yj {If 65 iih d7 6d dV 90 91 9^, 



M 



Fig. 2o6. 



The thick line shows the variations in January of the surface temperature off the west coast of Norway 



from year to year ; the thin line the variations of the air-temperature at Orebro (Sweden). 



surface-water corresponding to a high temperature in the air. 

 Pettersson further pointed out that a certain deviation from the 

 normal temperature of the air, as a rule, lasts for a length of 

 time ; a cold period, for instance, often lasts for weeks, or 

 even months. Now, there are many relations on the land 

 which are influenced by the deviations of the air-temperature 

 from the normal, among other things, the duration of the snow- 

 covering, the time of blossoming of many plants, the time for 

 beginning field-labour in spring. Pettersson found the varia- 

 tions in some of these particulars to agree with the variations 

 in the temperature of the air and of the surface-water off the 

 west coast of Norway some time before. Fig. 207 shows an 

 example of this agreement ; the lower curve gives the variations 



