METEOROLOGY AND ALLIED SUBJECTS. 315 



by unknown causes. In 1869 Silberman remarks, "All the phenonxMia 

 appear as if the aurora of 1859 and 1869 were simply thunder storms, 

 that discharged themselves not in lightnings but in steady streams 

 towards the upper region of the atmosphere. It appears that when 

 the globules of aqueous vapor in the lower strata of air are strongly 

 charged with electricity, and are for any reason carried towards the 

 upper region these globules crystalize in small ascending prisms, and 

 that their electricity, by reason of its steady flow from these ice-needles, 

 becomes visible as the auroral light. In this way the apparent ascen- 

 sion of the auroral beams is explained." 



Many of the advocates of the electrical hypothesis seek for the origin 

 of the electricity either in the earth or«the ocean. But a decision there- 

 upon is still in the distant future. Sirks, in 1873, seems to have been 

 the first to attribute the electric currents upon the earth to the direct 

 influence of the sun, which is the source of all forces upon this earth 

 as well as the other planets. Baumhauer, in 1844, suggested the 

 meteor-dust theory. According to this the higher regions of the 

 atmosphere are full of the dust particles from innumerable meteors 

 which become incandescent as they flow toward the magnetic poles. 

 Similar views are maintained by Foster, Schmidt, and others. If, now, 

 we compare the epochs at which the various theories and hypotheses 

 have arisen, we recognize at once that with every step of progress in 

 physics, astronomy, and chemistry, fresh impetus is given to the search 

 for the explanation of the phenomena. The meteorite theory could only 

 be developed lately, namely, since the doubt has been dissii)ated which 

 has for a long time existed as to the cosmic origin of the falling masses, 

 and since the meteor shower of 1833 has made us familiar with the regu- 

 lar recurrent ^ISrovember stream. Even now we have but just recognized 

 that planetary space is full of large and small bodies which enter into 

 the sphere of attraction of the earth and become visible as meteoric 

 stones. (Fritz, Das Polarlicht, Leipzig, 1881.) 



The diurnal change in magnetic declination at Greenwich has been 

 deduced by Karlinski from the annual observations published by the 

 Greenwich Observatory, as based on the photographic registers. The 

 I)riucipal maximum occurs between 1 and 2 p. m., and the general diur- 

 nal change is t>hown by the following table : 



iZ. 0. G. 3f., 1879, XVI, p. 60.' 



