PART I. : TEMPERATURE OBSERVATIONS IN THE MADUSEE, POMERANIA. 627 



effect of the wind was to make the discontinuity very sharp, and to make the water 

 above the discontinuity of practically uniform temperature. The same thing is shown 

 otherwise by the light line on fig. 3, which represents the range of temperature in the 

 first 10 metres from the surface at Moritzfelde — again taking means of each day's 

 observations. This diagram shows how rapidly the temperature gradient at the surface 

 increases during calm weather and how rapidly the water becomes mixed up during 

 strong winds, until there may be only '1° or •2° C. of difference between the temperature 

 at the surface and at a depth of 8 to 10 metres. 



§ 1 6. The temperature changes on 6th August are a little puzzling. Reference to 



















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TEMPER4TUPE DIFFERENCE FQOM THE SURFACE T >o METRES AT MO"IT2FELDE 



Fig. 3. 



Plate I. shows that a new series of oscillations was started on that date, and fig. 2 shows 

 a sudden decrease of the sharpness of the discontinuity and a simultaneous rise in the 

 surface temperature gradient. At the same time a strong wind was blowing, so the 

 lake behaved in an unexpected manner. But a closer examination of the observations on 

 5th, 6th, and 7th August gives the explanation. On 5th August the mean temperature 

 of the surface layers was about 19° C, and on 7th August 18° C. This is because the 

 wind was sufficiently strong to cause the discontinuity layer to rise to the surface at 

 the windward end. Therefore some of the colder water mixed with the bottom water, 

 and until this mixing process was complete there was a considerable temperature gradient 

 at the surface. After a short time we find the lake behaving in the usual manner. 



§ 17. The observations in the Madlisee have served the purpose for which they were 

 TRANS. ROY. SOG. EDIN., VOL, XLVII. PART IV. (NO. 22). 94 



