CONTENTS. Xxi 



COLLOIDS 



522. General properties of colloids * 406 



523. Molecular weights of colloids 406 



524. Brownian movement 406 



525. Adsorption of gas by finely divided particles 407 



526. Heats of adsorption 407 



527. Molecular heats of adsorption and liquefaction 407 



528. Miscellaneous constants, atomic, molecular, etc. ..." 408 



529. Radiation wave-length limits 408 



530. Periodic system of the elements (Mendelejeff) 409 



531. Atomic numbers 409 



532. Periodic system of the elements and radioactive isotopes (Hackh) . . 410 



ASTRONOMICAL DATA 



533. Stellar spectra and related characteristics 411 



534. The Harvard spectrum classification 411 



535. Apex and velocity of solar motion . ^ 411 



536. Motion of the stars 412 



537. Distances of the stars 412 



538. Brightness of the stars 413 



539. Masses and densities 413 



540. Miscellaneous astronomical data 414 



541. The first-magnitude stars ...... 415 



542. Wolf's observed sun-spot numbers, 1750 to 1917 415 



543. Length of degrees on the earth's surface 416 



544. Equation of time 416 



545. Planetary data " 416 



546. Numbers and equivalent light of the stars 417 



547. Albedos 417 



548. Duration of sunshine 417 



549. The solar constant 418 



550. Solar spectrum energy and its transmission through the atmosphere . 418 



551. Intensity of solar energy in various sections of spectrum 418 



552. Distribution of brightness (radiation) over the solar disk 418 



553. Transmission of radiation through moist and dry air (see Table 376) . 410 



554. Brightness of sky at altitudes of 1730 m and sea-level 419 



555. Relative distribution in normal spectrum of sun and sky light . . . 419 



556. Air masses 419 



557. Relative intensity of solar radiation for various months 420 



METEOROLOGICAL DATA 



558. Mean monthly and yearly temperatures for representative stations . 420 



559. The earth's atmosphere, variation with latitude, miscellaneous ... 421 



