860 



SCIENCE 



[N. S. Vol. XXX. No. 781 



The extremely uncertain value of the ef- 

 fects, the irregularity and impossibility of 

 calculation or prediction, render the prob- 

 lem of protection difficult. The effects of 

 these secondary surges are generally incom- 

 parably less violent than direct strokes, and 

 they are seldom dangerous to life. 



So long indeed as our electric lines are 

 extended above the ground, so long must 

 this disturbing factor be reckoned with. 

 Fortunately it has been possible by con- 

 stant effort and study to secure more and 

 more effective appliances so that the light- 

 ning menace grows steadily less. Research 

 and experimentation in this direction have 

 constituted an important part of the devel- 

 opment of electrical engineering. 



Having thus at some risk of your pa- 

 tience vindicated our earliest worker in the 

 study of atmospheric electricity— Franklin 

 — let us turn from the practical issues and 

 consider the electricity of the air from a 

 more general standpoint. 



The study of the nature and origin of 

 electrical storms or disturbances through- 

 out the atmosphere is of much interest; 

 our knowledge is yet meager ; there is much 

 more yet to be learned in this fascinating 

 field. Exploration of the electrification of 

 the air at varying heights by captive bal- 

 loons, by kites and upon elevations of land, 

 has generally shown an increasing electric 

 potential upward from the earth, and usu- 

 ally positive in relation thereto. Sometimes 

 this relation is reversed. It has been 

 roughly estimated that if the differences 

 noted can be assumed to be extended to 

 include the total depth of the atmospheric 

 layer, the earth's surface might be negative 

 to the surrounding space, 150,000 volts 

 more or less. This condition would not 

 admit of being regarded as constant or 

 stable, since widespread electric storms 

 occur in both our upper and lower air 

 levels. In the highest regions of our at- 



mosphere they take the form of diffuse dis- 

 charges as in a high vacuum and are called 

 auroras. They either accompany or give 

 rise to magnetic storms, which affect the 

 direction and intensity of the earth's mag- 

 netism temporarily, and hence disturb the 

 compass needle, sometimes through many 

 degrees. Within a few weeks past we have 

 experienced such a storm of a remarkable 

 intensity; sufficient in fact to cause inter- 

 ruptions to telegraphic and cable transmis- 

 sion during several hours. Brilliant au- 

 roras Avere at the time seen in some places. 



The frequency of auroral phenomena, 

 and perhaps also to some extent the fre- 

 quency of thunder-storms, seems to keep 

 pace with the sunspot period, at least in 

 our latitudes. At times of sunspot activ- 

 ity, the surface layers of the sun, upon 

 the energy radiated from which so much 

 of earthly activity depends, are stirred by 

 great storms, or immense cyclones of hot 

 gas or metallic vapors; storms seen as 

 dusky spots on the sun's disc. They can 

 attain enormous size— 20,000, 30,000 or 

 even 50,000 miles in diameter, though these 

 dimensions are exceptional. They are vis- 

 ible, as is well known, not because they are 

 non-luminous, but because they are less 

 luminous than the surrounding solar sur- 

 face. In like manner bright spots or fac- 

 ulce may also be seen, because they are on 

 the whole brighter than the sun's surface 

 adjoining them. 



There is much reason to believe that, in 

 accordance with suggestions made many 

 years ago, these solar storms are accom- 

 panied by exceptionally vigorous projec- 

 tion outward from the sun to immense dis- 

 tances, of streams of electrified matter. 

 Should the earth happen to be in a position 

 to be swept by such a stream, an aurora 

 may be produced. During a total solar 

 eclipse the so-called coronal streamers are 

 seen to extend from the sun's surface to 



