A CENTURY'S PROGRESS IN PHYSICS 389 



ing points of lowest pressure, he drew a curve through all 

 points where the barometer stood at its normal level, then 

 one through those points at which the pressure was 2/10 

 of an inch below normal, and so on. Temperature he 

 treated in much the same way, and the strength and 

 direction of the wind were indicated by arrows. This 

 innovation gave to his storm analyses a significance 

 which had been entirely lacking in those of his predeces- 

 sors, and led to the familiar systems of isobars and iso- 

 therms in use on the daily charts issued by the Weather 

 Bureau at the present time. Loomis advocated careful 

 observations for one year at stations 50 miles apart all 

 over the United States, so that sufficient data might be 

 obtained to settle once for all the law of storms. His 

 efforts, seconded by those of Henry, Bache, Pierce, Abbe, 

 and Lapham, led eventually to the establishment of the 

 Signal Service, and the publication of daily weather 

 maps according to the plan advocated thirty years 

 before. These maps afforded a basis for further 

 analyses of storms, which he published in numerous 

 "Contributions to Meteorology" (8, 1, 1874, et seq.) 

 between 1874 and his death in 1890. 



In addition to his work on storms, Loomis made a care- 

 ful study of the earth's magnetism (34, 290, 1838 et seq.), 

 and of the aurora borealis (28, 385, 1859 et seq.). That 

 a connection existed between sunspots, aurora, and ter- 

 restrial magnetism was already recognized. Loomis (50, 

 153, 1870 et seq.), however, showed that the periodicity 

 of the aurora borealis, as well as of excessive disturb- 

 ances in the earth's magnetic field, corresponds very 

 closely with that of sunspots. 



Notes* 



1 J. W. Gibbs, Trans. Conn. Acad. Arts and Sci., 3, 108 and 343. Abstract 

 by the author, the Journal, 16, 441, 1878. 

 2 H. K. Onnes, Nature, 93, 481, 1914. 

 8 H. Hertz, Wied. Ann., 34, 551, 1888 et seq. 

 4 E. F. Nichols and G. F. Hull, Phys. Eev., 13, 307, 1901 et seq. 

 B J. J. Thomson, Phil. Mag., 44, 293, 1897. 

 E. A. Millikan, Phys. Eev., 2, 109, 1913. 



7 P. Zeeman, Phil. Mag., 43, 226, 1897. 



8 H. A. Lorentz, Phil. Mag., 43, 232, 1897. 



S. J. Barnett, Phys. Eev., 6, 239, 1915, and 10, 7, 1917. 

 10 W. C. Eontgen, Wied. Ann., 64, 1, 1898 et seq. 



