June 3, 1910] 



SCIENCE 



877 



The distribution of plants in salt marshes and 

 along salt-water estuaries is determined by the 

 percentage of salt in the water and in the soil. 

 This can be estimated indirectly by a hydrometer 

 reading directly the specific gravity of liquids 

 heavier than distilled water, the readings being 

 afterwards reduced to percentages of salinity. 

 This specific gravity can be determined for each 

 salt marsh and saline species of plants by collect- 

 ing the water at the roots of the plants and esti- 

 mating its salinity by hydrometer with a ther- 

 mometer attachment. By this means the transi- 

 tion from salt-water to fresh-water vegetation 

 can be studied. 



Solar Activity and Terrestrial Magnetic Disturh- 



amces: L. A. Batjee, Washington. 



A recent examination of the times of beginning 

 of magnetic disturbances, as recorded at observa- 

 tories over the entire globe, showed that, without 

 doubt, magnetic storms do not begin at absolutely 

 the same instant of time, as heretofore believed. 

 Instead, they progress around the earth, the times 

 generally increasing as we go around the earth 

 eastwardly; for the quick and abrupt disturb- 

 ances, which are usually comparatively minute in 

 their effect on the compass needle, the complete 

 passage around the earth requires from three to 

 four minutes. For the bigger effects or for the 

 greater magnetic storms, the rate of progression 

 is slower, so that it would take them a half hour 

 or more to get around the earth completely. 

 There is thus introduced a new point of view in 

 the investigation of the origin of magnetic storms. 



In addition to negatively charged electrified 

 particles coming from the sun to which recent 

 theories souglit to attribute our magnetic storms, 

 but which the speaker found would produce ef- 

 fects not in harmony with those actually observed, 

 we also receive radiations such as the Rontgen 

 rays, for example, which are not defiected by the 

 earth's magnetic field as they do not carry electric 

 charges. Their chief efi'ect will be to ionize the 

 gases of which the atmosphere is composed, i. e., 

 make the air a better conductor of electricity. 

 Ultra-violet light has the same effect. It is known 

 that a small part of the magnetic forces acting on 

 a compass needle is due not to the magnetism or 

 electric currents below tlie earth's surface, but to 

 electric currents already existing in the atmos- 

 phere and which the speaker showed were brought 

 about by the atmosphere cutting across the earth's 

 lines of magnetic force in its general circulation 

 around the globe. If the regions of these upper 



electric currents are at any time made more con- 

 ducting by some cause, electricity will be imme- 

 diately set in motion, which in turn affects our 

 compass needles. 



This new theory, called " the ionic theory of 

 magnetic disturbances," satisfactorily explains the 

 principal features of magnetic storms. As the 

 currents get lower down in the atmosphere their 

 velocity is checlced, so that instead of taking but 

 three to four minutes to circulate around the 

 earth, as do the higher currents, it may take them 

 a half hour and more; however, their actual effect 

 on the magnetic needle would be greater because 

 of their coming nearer to the earth. The theory 

 also opens up the possibility of accounting for 

 some of the other changes and variations experi- 

 enced by the earth's magnetism, and likewise has 

 a bearing on the peculiar formation of the mag- 

 netic fields in sunspots discovered by Professor 

 Hale. 



Magnetic Results of the First Cruise of the " Car- 

 negie " : L. A. Batjee, Washington. 

 The non-magnetic vessel Carnegie completed on 

 February 17 last the first cruise, covering in all 

 since September 1, 1909, 8,000 miles. Special 

 tests made at Gardiners Bay, Long Island, and 

 at Falmouth, England, proved conclusively that 

 there are no corrections to the magnetic instru- 

 ments of the kind encountered on vessels in which 

 more or less iron occurs in the construction. Thus 

 in a single voyage errors could be disclosed in the 

 compass charts used by mariners on their trans- 

 atlantic voyages of importance not alone from a 

 scientific standpoint, but from that of practical 

 and safe navigation as well. 



The errors found by the Carnegie in the declina- 

 tion at various points along the track followed 

 by the vessel from Long Island Sound to Fal- 

 mouth, England, amounted on the average to 

 about 1 degree — an error which persisted in the 

 same direction for long distances. 



After leaving Falmouth, the Carnegie headed 

 for Funchal, Madeira. Thence she sailed to 

 Bermuda, and finally arrived at Brooklyn, Feb- 

 ruary 17. In spite of the unusually adverse con- 

 ditions frequently met with during this first 

 cruise, more or less extensive magnetic observa- 

 tions were secured almost daily. 



The errors of the compass charts were found 

 in general even more pronounced for the southerly 

 half of the cruise, viz., Madeira to Bermuda, than 

 for the northerly half, and were again shown to 

 be systematic in their nature. Some of the charts 

 were in error two to three degrees. 



