Xxii CONTENTS. 



560. Variation of percentage composition with altitude, pressure .... 421 



561. " " temperature, pressure and density with altitude .... 421 



562. Temperature variation over the earth's surface 422 



563. " " with depth, land and ocean 422 



564. Geochemical data. Meteorites 423 



Geodetical Data 



565. Acceleration of gravity, sea-level and different latitudes and 



altitudes 424 



566. Gravity as observed at various stations and reduced to sea-level. . . 425 



567. " corrected to sea-level and for topography and compensation. 426 



568. Length of seconds pendulum, sea-level and various latitudes .... 427 



569. Miscellaneous geodetic data 427 



Terrestrial Magnetism 



570. Secular change of declination, 1 810 to 1920 428 



571. Dip or inclination, various longitudes and latitudes, 1915 430 



572.' " " " secular change, 1855 to 1915 430 



573. Horizontal intensity, various longitudes and latitudes, 191 5 .... 431 



574. " " secular change, i860 to 1915 431 



575. Total intensity, various longitudes and latitudes 432 



576. " " secular change, 1855 to 1915 432 



577. Agonic line, 1800 to 1915 433 



578. Mean magnetic character by months and years, 1906 to 1917 . . . 433 



579. Recent values of the magnetic elements at magnetic observatories . . 434 



Appendix, dft^tnttions 435 



Table 580. Temperature measurements 438 



" 581. Adsorption of H and He by cocoanut charcoal 439 



" 582. Adsorption by charcoal at low pressures and temperatures 439 



" 583. Adsorption of hydrogen by palladium black 439 



" 584. Audibility of sound ; f (pressure and frequency) .... 440 



" 322. Spectrum series (concluded from p. 275) 441 



" 518. Ionizing and resonance potentials (concl'd from p. 403) . 442 



" 585. List of stars known to be within five parsecs 443 



Index 445 



The following tables appearing in the 6th revised edition of these fables have been omitted: 

 Table 222. Newton's rings; thicknesses corresponding to various colors. 



" 292. Ratio of the electrostatic to the electromagnetic unit of electricity = v (historical). 

 " 293. Absolute measurement of currents and the E.M.F. of standard cells (historical). 

 " 295. Contact difference of potential in volts ; solids with liquids and liquids with liquids. 

 " 305. Various determinations of the ohm (historical). 



I 



