376 . EXPEDITION TOWARD THE NORTH POLE. 



of quinine. By thus condensing tlie light on the paper, any flaores- 

 cense which the ray may contain will be indicated by the appearance of 

 the previously invisible characters in a green color. 



Careful observations should be made to ascertain whether the aurora 

 ever appears over an expanse of thick ice, or only over land or open 

 w^ater, ice being a non-conductor of electricity. 



The question whether the aurora is ever accompanied with a noise has 

 often been agitated, but not yet apparently definitely settled. • Atten- 

 tion should be given to this point, and perhaps the result may be 

 rendered more definite by the use of two ear-Lrumpets, one a))plied to each 

 ear. 



According to ITansteen, the aurora consists of luminous beams, par- 

 allel to the dipping needle, which at the time of the formation of the 

 corona are shooting up on all sides of the observer, and also the lower por- 

 tions of these beams are generally invisible. It is, therefore, interesting 

 to observe whether the auroral beams are ever interposed between the 

 observer and a distant mountain or cloud, especially when looking 

 either to the east or west. 



The effect of the aurora on the magnetism of the earth will be ob- 

 served by abnormal motion of the magnetic instruments for observing 

 the declination, inclination, and intensity. This effect, however, may 

 be more strikingly exhibited by means of a galvanometer, inserted near 

 one end of a long insulated wire extended in a straight line, the two 

 extremities of which are connected with plates of metal plunged in the 

 water, it may be through holes in the ice, or immediately connected 

 with the ground. 



To ascertain whether the effect on the needle is due to an electrical 

 current in the earth, or to an inductive action from without, perhaps the 

 following variation of the preceding arrangement would serve to give 

 some indication. Instead of terminating the wire in a plate of metal, 

 plunged in the water, let each end be termiimted in a large metallic in- 

 sulated surface, such, for example, as a large wooden disk, rounded at 

 the edges and covered with tin-foil. If the action be purely inductive, 

 the needle of the galvanometer inserted, say near one end of the wire, 

 would probably indicate a momentary current in one direction, and an- 

 other in the opposite, at the moment of the cessation of the action. For 

 the purpose of carrying out this investigation the Smithsonian Institu- 

 tion has furnished the expedition with two reels of covered wire, each a 

 mile in length, one of which is to be stretched in the direction, perhaps, 

 of the magnetic? meridian, and the other at right angles to it. It would 

 be well, however, to observe the effect with the wires in various direc- 

 tions, or united in one continuous length. 



Elcctriciiy. — From the small amount of moisture in the atmosphere, 

 and the consequent insulating capacity of the latter, all disturbances of 

 the electrical equilibrium will be seen in tlie frequent production of 

 light and sparks on the friction and agitation pf all partially uon con- 



