452 



NATURE 



[March 9, 1899 



Bill constituting the central aiilhorily this year, to introduce one 

 for the constitution of local authorities next year. 



The question of the relations of the proposed Board of 

 Education to the Charity Commissioners was an extremely diffi- 

 ■ cult one. He thought the provisions relating to the subject 

 in the Bill of this year might probably differ in some respects 

 from those in last year's Bill ; and he hoped that any alterations 

 that might be made in them might be in the direction which the 

 deputation had indicated and appeared to desire. He did not 

 anticipate much difficulty in obtaining assent to the general 

 principle of the Bill. When they came to its details he had no 

 doubt that some difference of opinion might be developed, and 

 he would be very happy to have an opportunity of taking the 

 advice of some of the gentlemen who composed the deputation, 

 and who would be so competent to render it. 



THE ORIGIN OF ATMOSPHERIC 

 ELECTRICITY} 



A LMOST every- suggestion that has ever occurred to any one 

 ■^^ as to the origin of atmospheric electricity, and the part it 

 plays in meteorology, has been tested over and over again during 

 the past century with only negative results. Some of these are 

 noted in the following paragraphs : 



Volta and De Saussure suggested the evaporation of the 

 natural waters on the surface of the globe, all of which are more 

 or less impure, but Pouillct showed that electricity could not 

 come from the evaporation of pure water, but might come from 

 salt water and also from the evaporating surfaces and chemical 

 changes incident to vegetation. De la Rive showed that veget- 

 ation was entirely insutticienl.and Uei.ss showed that evaporation 

 of salt water does not, of itself, produce electricity ; on the other 

 hand, he showed that the friction of drops of water against the 

 sides of a platinum vessel would produce a small amount. 



The hypothesis that our electricity comes from the action of 

 the sun in heating the atmosphere, as also that it is produced by 

 the friction of warm air against cold air, have both been 

 examined, but experiment has never been able to demonstrate 

 the slightest trace of thermo-electricity in gases and vapours. 



Schoenbcin considered that the oxygen of the air might act 

 electro-chemically upon the molecules of water of which the 

 clouds are composed ; but this again has received no experi- 

 mental confirmation, and could hardly account for the electricity 

 that we find in the clearest dry air. E. Becquerel suggests the 

 decomposition of organic matters ; but this, also, is not con- 

 sidered sufficient. It is recognised on all sides that the 

 evaporation of terrestrial waters may carry the negative electricity 

 at the surface of the ground upwards into the atmosphere ; but 

 this does not explain the origin of that electrified state at the 

 surface, nor the tact that the atmosphere remains positive while 

 the earth remains negative. 



De la Rive considered that the continual chemical action 

 taking place in the interior of the globe explains the origin 

 of terrestrial electricity, and that, as beneath the ocean this 

 action is due to infiltration of sea water, therefore, the ocean 

 is charged with positive electricity, but the solid continents 

 with negative. Kspecially in the equatorial regions would 

 the atmosphere receive from the sea those positively electri- 

 fied vapours which, after overflowing into the two hemi- 

 spheres, would descend in the polar regions and produce 

 auroras, lightning, &c. But this fascinating and comprehen- 

 sive theory seems to be not at all in harmony with the recent 

 careful observations as to the nature of the electrical distri- 

 bution in latitude and over oceans anil continents. It is 

 generally acknowledged that a great amount of electrified vapour 

 and dust is carried up in every volcanic eruption : but although 

 the quantity is enormous, yet it is not sufiicicnt to explain the 

 condition of the whole atmosphere, although we may thereby 

 explain some of the variations in its general electrified con- 

 dition ; this volcanic electricity apparently originates in a variety 

 of ways, especially from friction. 



The fact that a magnetised body when in motion gives rise 

 by induction to an electric current flowing through a neighbour- 

 ing conductor has led Rowland and S. I'. Thom|>son to calculate 

 the electric effect of motions, such as the wind blowing over the 

 surface of a magnetised globe, or the effect of the rotating mag- 

 netic earth upon the ether of space in its neighbourhood. But 

 here again the electric effect turns out to be too small. 



■ By Prof. Cleveland .\bbc. (Reprinted from the U.S. Mcnlkly Wtalhet 

 Xrt'im. }unK: 1898.1 



NO. 1532, VOL. 59] 



The discovery by Arrhenius that sunlight, especially the ultra- 

 violet rays, greatly diminish the insulating power of dry air and 

 produce what is called photo-electric dissipation and the pheno- 

 mena discovered by Hallwachs, that a conductor carrying a 

 negative charge gives it up to the surrounding gas when struck 

 by a ray of ultra-violet light, have given rise to the idea that in 

 this way the sunlight acting upon one-half of the earth's atmo- 

 sphere may discharge the electricity therefrom as well as from 

 the earth and ocean beneath the air ; but this, again, has not 

 yet been demonstrated by experiment. 



Faraday and Solmcke have shown that dry crystals of ice, 

 such as may occur in the coldest dry air, may become positively 

 electrified by friction, as, for instance, by descending through 

 the air, and Sohncke has formulated a theory explanatory of the 

 electricity of thunderstorms as dependent upon the behaviour of 

 cirrus and cumulus clouds. The electricity is generated in the 

 region of the isothermal surface of 32° F., but this ingenious 

 view still wails for its confirmation. Brillouin has advanced aiv 

 ingenious explanation of the origin of atmospheric electricity, 

 based upon the action of ultra-violet light upon the crystals of 

 ice that constitute cirrus clouds (see Monthly Weather KevUvr 

 for 1897, p. 440), but some points in his theory remain to be 

 established by further experimentation. P. de Heen suggests 

 that as solar radiation illuminates .ind heats the earth, so it also 

 has the power to electrify the upper strata of air ; that these, in 

 fact, as it were, absorb the electric influence, and then, being 

 electrified, act indirectly on the ground below. Maclean and 

 Lenard have .studied the electrification of the air by drops of 

 water falling through it. It is found that falling water drops 

 give the air a negative charge, but so also do snow crystals ; 

 therefore the higher strata of air .should be negative instead of 

 positive, as actually observed. Marvin observes that a rain of 

 fine drops of mercury in dry air electrifies the drops and pre- 

 .sumably the air. I'almieri has shown that the condensation of 

 aqueous vapour in and of itself does not develop electricity. Gay 

 Lussac and I'ouillet did the same for all changes of condition 

 from solid to fluid to vapour to gas, and the reverse ; no elec- 

 tricity is developed except in the change from fluid to solid, 

 when some solids, such as sulphur, show slight manifestations 

 which are due to the action of the edge of the solidifying liquid 

 on the glass vessel containing it. 



The inductive action of the earth on its atmosphere is un- 

 doubtedly important, but the action of the sun, distant as it is, 

 may be appreciable. Kdlund and Siemens have advocated the 

 solar origin of atmospheric electricity, but their hypotheses have 

 not yet been generally accepted. 



The spre,id of the electro-magnetic telegraph lines and the 

 electric cables over the globe has shown that local electric cur- 

 rents generally (lowing in an east-west direction exist everywhere 

 in the earth, thus suggesting that the electrified condition of the 

 atmosphere depends upon them. Clerk Maxwell, in his treatise 

 on electricity, after recognising that all other sources are in- 

 sufficient, suggests that possibly the changing pressures to which 

 the earth's crust is subjected by tidal strains m.ay give rise to 

 piezo-electriciiy sufficient to expkin the negative charge of the 

 earth ; the editor, quite independently of Maxwell, has elaborated 

 this hypothesis in his " Preliminary Studies." The laws of these 

 tidal strains have been studied by Chrce, Davison, Darwin, and 

 others. 



The thermo-ckciric currents of Peltier and the piezoelcc- 

 tricity so fully investigated by Gaugain are not suflicient ti> 

 explain the amount of electricity represented by the currents 

 flowing through the earth's .surface, but the piezo-electric 

 currents due to lidal strain may be quite sufficient. The lattei 

 represent the conversion of gravity into electricity. 



Lord Kelvin, without touching the question .is to the ultimate 

 origin of the eleclrilicd state, shows that observed phenomena 

 are sufficiently explained by simply recognising the fact that the 

 atmosphere can be treated as the dielectric of a condenser (like 

 the glass between the two sheets of tinfoil in a Leyden jar) ; the 

 lower or earth's surface is negative, and the upper layer of the 

 atmosphere is positively electrified. 



But without pursuing further the maze of hypotheses as to the 

 ultimate origin of the electrified state of the iilmosphere, we 

 must conclude that this problem is too ditlicult for mimediate 

 solution ; it is one of many that a following generation of 

 physicists will undoubtedly cope with successfully. 



If we turn lo the simpler question of the meteorological 

 phenomena that are evidently .-ussocialed with atmospheric elec- 

 tricity, we shall tind that the best physicists are not yet wholly 



