XIII 



Page 



Cloud Motion 522 



Cirrus Belts 525 



Precipitation 526 



Probability. Diurnal Period 526 



Annual Period 527 



Wind-Roses 528 



Number of Days with Precipitation 531 



Duration of Periods with Precipitation 533 



Duration of Precipitation in one Day of Precipitation 534 



Amount of Precipitation 534 



Fog 536 



Diurnal Period of the Probability of Fog 536 



Annual Period 537 



Number of Days with Fog 537 



Optical Phenomena 538 



The Temperature of the Polar Ice 540 



Observations 544 



Summary 560 



Annual Period 561 



Variation with Depth 562 



Isopleths 567 



The Distribution of atmospheric Pressure and Temperature around the 



North Pole 570 



Isobars 571 



Isotherms 573 



Mean monthly Temperature at the North Pole 574 



The annual Migration of the Isotherm for C 575 



Normal Temperatures for Latitudes 60 to 90 N 575 



[subnormals 576 



Barometrical Depressions and their Motion 577 



Tables 579 



Numbers of Depressions 581 



Lowest Pressure in Depressions 581 



Centres of Depressions passing the Fram 582 



Velocity of the Wind 583 



Direction of Motion of Centres 583 



Velocity 586 



The diurnal and annual Periods of the meteorological Elements in the 



arctic circumpolar Sea 588 



Twilight 589 



Distance to the Shadow of the Earth 592 



Thermal Radiation 593 



Velocity of the Wind 597 



Temperature of the Air 603 



