METEOROLOGY AND ALLIED SUBJECTS. 317 



That this process depends principally upon the temperature to which 

 ^he air is heated is evident from the fact that when the wire is of a dark 

 red incandescence no transfer of electricity takes place; it is with the 

 bright red glow that the air first begins to be charged. Nahrwold 

 further concludes that the charge cannot be increased indefinitely, but 

 approaches a maximum limit. He also observed a diflference in the be- 

 havior of the air with respect to the two forms of electricity — it takes 

 a positive charge easier than a negative one. 



When two crowns, composed of thirty-four knittiug needles, were 

 placed upon the base of the apparatus by which the electricity could be 

 conducted to the earth, it appeared that these points hastened the dis- 

 €harge of electricity, or the loss of the original charge only when the 

 air was filled with dust, which further proves that tbe so-called influence 

 of such points is largely dependent upon the dust contained in the air. 



From a few experiments which gave a strong negative charge to the 

 iiir after stirring up the dust on the floor of the room, Nahrwold con- 

 cludes that the dust becomes electrified by friction, and he concludes 

 his memoir as follows: "If the electricity of the dust depends, even 

 only in part, upon friction, and is therefore at least in part independent 

 of the distribution of atmospheric electricity properly so called, then in 

 observations of atmospheric electricity this must be considered as in mo.st 

 cases a not unimportant source of error and must necessarily be avoided. 

 In this condition, most difficult to fulfill, we see a new obstacle in the way 

 of attaining a clear idea as to the electrical processes in our atmosphere, 

 and we find ourselves no nearer the attainment of the object of our labors 

 through the results of the present investigation. 



"The method here employed is, however, certainly the least unsafe. 

 The observations here given are in their meteorological aspects scarcely 

 more than preliminary trials for a far more important investigation, 

 which will ultimately lead us nearer to the object in view. 



"Those conditions that most probably exercise an important influence 

 on the electrical condition of our atmosphere must be realized on a small 

 scale, and I hope ere long to be in the condition to again prosecute this 

 work in this direction." {Z. 0. G. M., XIV, 1879, p. 72.) 



Weyprecht, in the Denkschri/ten of the Vienna Academy (Vol. 

 XXXV), gives the results of his aurora observations. He classifies 

 the optical appearances, first, as arcs; second, as streamers; third, as 

 rays; fourth, as corona; fifth, as haze. To these forms there is also to 

 be added a dark, narrow, low standing arc of light, whose center coin- 

 cides nearly with the magnetic meridian, and which he calls the dark 

 segment. The movements of the auroral light are classified as follows: 

 first, waves; second, flashes. As to the height of the aurora Weyprecht 

 concludes that even in the arctic regions this is very variable, but 

 much lower than in our latitudes. The appearance of the aurora is as 

 though its light were dependent on that from some other matter. Xo 

 connection can be made out between the aurora and the subsequent 

 weather, neither can any noise be heard attending the aurora; a slight 



