CONTENTS XXV11 



740. Dip or inclination, United States [1925, long, and lat. variation] . . 592 



741. Secular change in dip, United States [1855-1925] 592 



742. Horizontal intensity, United States [1925, long, and lat. variation]. 593 



743. Secular change in horizontal intensity, United States [1855-1925]. 593 



744. Total intensity, United States [1925, long, and lat. variation] . . 594 



745. Secular change in total intensity, United States [1855-1925] . . . 594 



746. Agonic line, United States [1800 to 1925] 595 



747. Mean magnetic character of each month, 1906 to 1930 595 



Atmospheric Electricity 



748. Elements and constants of atmospheric electricity 596 



749. Atmospheric-electric data 596 



750. Ionic equilibrium in the atmosphere 597 



751. Thunderstorm electricity 598 



752. Charge on rain and snow 598 



753. Ionization in the upper atmosphere of the earth 599 



754. Ion density y+ in the upper atmosphere 599 



754(a). Maximum electron density y, max. in the upper atmosphere . . 600 



Astronomy 



755. Miscellaneous astronomical data 601 



756. " and formulae 602 



757. Calendar, Julian day 603 



758. perpetual 603 



759. Right ascension-declination into galactic coordinates 604 



760. Planetary data 606 



761. Satellites of the solar system 606 



762. Diameters of the planets 606 



763. Planetary and Satellite distances, Bode's law ; later developments . 607 



764. Albedos 607 



765. Equation of time 607 



766. Solar data : The solar constant 608 



767. Solar spectrum energy, transmission by earth's atmosphere . . 608 



768. Amount of solar radiation, u.-v., visual, i.-r., in calories . . . 608 



769. Distribution of intensity (radiation) over the solar disk . . . 608 



770. The solar constant, decade means 609 



77 l - monthly and yearly means 609 



77?- " " " 1930, 1931 610 



773- Wolf's observed sun-spot numbers. Annual means 610 



774. Duration of sunshine 610 



775. Transmission of radiation through moist and dry air . . . .611 



776. Brightness of sky radiation, Mt. Wilson (1730 m.), Flint 



Island (sea-level) . . . ; 6n 



