NO. 17.] BAROMETRICAL DEPRESSIONS AND THEIR MOTION. 587 



From these data we get Q = 1/82 mm. per meridian degree, and x = ll'OO 

 meridian degrees or 1222 kilometres. The diameter of the depression is 4a? 

 or 4889 kilometres. Generally the centre passes on one side of the Fram, 

 and the depression travels only along a chord of its circumference. Con- 

 sidering this circumference to be circular, and the distance of the chord equal 

 to x, the length of the chord is 4a; X sin 60 or 866 X ^ or 3'464, or 

 4233 kilometres. This chord is traversed in 4 days, or 96 hours. The rate 

 of propagation is 4233 : 96 or 44 kilometres an hour, or 12'2 metres per second. 



Taking separately the 10 cases in which the centre has passed the Fram, 

 we get a rate of 54 kilometres an hour, or 15 metres per second (b = 751'6 mm.; 

 y = 751 6 742 3 = 93 mm. ; t = 25'3; v = 89 m. p. s. ; G = 1 675 ; 

 x = 11- 10. Duration = 3'8 days). 



In our European depressions, we frequently have a rate of 40 km. per 

 hour (11 m. p. s.), and 90 km. an hour (25 m. p. s.) has been found several 

 times. In North America we have on an average 12'8 m. p. s., on the North 

 Atlantic Ocean 8'1 m. p. s., and in Europe 7'5 m. p. s. In Europe, the mean 

 rate is greatest 9 to 10 m. p. s. - - between Iceland and Norway, and 

 least - - 6 m. p. s. - - in Finland. 



The above-calculated rates for the Arctic Ocean - - 12 to 15 m. p. s. - 

 are of the same order as those found by means of synoptic charts in other 

 parts of the globe. 



