132 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



land, implying, of course, the establishment of a permanent 

 hydrographic commission ; second, that the most stringent 

 laws be enacted to prevent the willful unnecessary destruc- 

 tion of forests; and, third, that every thing be done that is 

 possible to encourage the planting and cultivation of forests; 

 and, finally, that the streams and rivers, as they at present 

 exist, be connected into a system by means of which the 

 height of the water may be regulated, and the traffic therein 

 facilitated as much as possible. Zeitschrift des Ingen,- U7id 

 Architekten-Vereins, p. 137. 



MAGNETIC PARTICLES IN ATMOSPHERIC DUST. 



The atmospheric dust examined by Tissandier was col- 

 lected in several different ways, and in every case was foimd 

 to contain minute magnetic ferruginous particles. Part of 

 the dust was collected upon sheets of paper exposed to the 

 air for many days ; in another series of experiments air was 

 passed through pure water, and the latter evaporated over 

 sulphuric acid in vacuo. Other samples were collected from 

 rain and snow water, in one instance, particularly, from snow 

 gathered upon Mont Blanc, 2712 meters above sea-level. The 

 ferruginous particles occurring in these various specimens of 

 dust were extracted by means of a magnet and subjected to 

 microscopic examination. In diameter they rarely exceed 

 T-^-jj of a millimeter, and appear to consist of magnetic oxide, 

 resulting from the combustion of iron. Tissandier believes 

 them to be of cosmical, not terrestrial origin, and regards 

 them as the debris of meteoric masses. 6 Z>, 1875, Oct. 4. 



ON THE HEIGHT OF THE AURORA BOREALIS. 



In discussing observations made by himself upon the 

 aurora during the Swedish expedition of 1868 to the North 

 Pole, Professor Lemstrom, of Helsingfors, states that al- 

 though Loomis, and even Bravais, believed that observations 

 which give a very low height to the aurora are erroneous, 

 and the result of some illusion, yet he can not agree with 

 them ; and he offers in support of his opinion, among other 

 things, the phenomena observed on the 18th of October, 

 1868, at the entrance of the Norwegian Archipelago, when 

 the whole horizon was covered with rays which were soon 

 united around the magnetic i)ole, forming a regular crown. 



