44 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



tions the solar spots arc in reality cavities, by which the hy- 

 drogen, and the various substances composing the solar at- 

 mosphere, escape from the photosphere, this hydrogen being 

 the result of a decomposition, bringing with it positive elec- 

 tricity, which is distributed in the planetary spaces, diminish- 

 ing in intensity more and more toward the earth, in conse- 

 quence of the poor conducting power of the more and more 

 dense strata of the air, and of the superficial crust of the 

 earth, this latter being negative only because it is less posi- 

 tive than the air. 



For this electricity to be propagated in any medium, some 

 substance is necessary as a vehicle ; and it is established, in 

 fact, that the luminous properties of electricity belong in a 

 great degree, if not entirely, to the ponderable matter across 

 which the electric discharges are transmitted. The auroras 

 result from the discharges of this electricity, thus explaining, 

 according to M. Becquerel, the rustling or crackling sound 

 heard by the inhabitants of the polar regions. This occur- 

 rence, although apparently well attested, has been denied by 

 some ; but the experience of M. Rollier, the intrepid aeronaut 

 who was carried in his balloon last December from Paris to 

 Norway, and landed upon a snow-covered mountain 10,000 

 feet high, confirms this view. This gentleman remarks, in 

 his report of the voyage, that while passing through a thin 

 fog he perceived the brilliant rays of an aurora tinging every 

 thing with its strange light. Very soon a curious and incom- 

 prehensible roaring was heard ; but this, after a time, ceased 

 entirely, with the development of a decided odor of sulphur, 

 which was almost suffocating. 3 J5, 1811, August 10, 172. 



DUKATIOX OF VISION. 



Professor Ogden N. Rood, of Columbia College, in a late 

 number oi SillimarCs Journal has an article upon the amount 

 of time necessary for vision, and refers to an experiment of 

 Wheatstone, which seems to show that distinct vision is pos- 

 sible in a period of less than one millionth of a second. He, 

 however, refers to experiments of his own, by which electric 

 sparks were produced whose duration was only the forty bil- 

 lionth part of a second; and yet, during their continuance, 

 the letters on a printed page were plainly to be seen ; and in 

 polariscope observations the cross and rings around the axis 



