EXPEDITION TOWARD THE NORTH POLE. 377 



ducting' substances. Any unusual occurrences of this kind, such as 

 electrical discharges from pointed rods, from the ends of spars, or from 

 the fingers of the observer, should be recorded. 



A regular series of observations should be made on the character 

 and intensity of the electricity of the atmosphere by means of an elec- 

 trometer, furnished with a polished, insulated, metallic ball, several 

 inches in diameter, and two piles of Deluc to indicate the character of 

 the electricity, whether -f or — ; and also supplied with a scale to 

 measure by the divergency of a needle the degree of intensity. This 

 instrument can be used either to indicate the electricity of the air bj^ 

 induction or by conduction. In the first case it is only necessary to 

 elevate it above a normal i>lane by means of a flight of steps, say eight 

 or ten feet, to touch the ball at this elevation and again to restore it to 

 its first position, when it will be found charged with electricity of the 

 same character as that of the air. Or the ball may be brought in con- 

 tact with the lower end of an insulated metallic wire, to the uj)per end 

 of which is attached a lighted piece of twisted paper which has been 

 di'ied after previous saturation in a solution of nitrate of lead. 



Thunder-storms are rare in the Arctic regions, although they sometimes 

 occur; and in this Case it is important to observe the point in the hori- 

 zon in which the storm-cloud arises; also the direction of the wind dur- 

 ing the passage of the storm over the place of the observer ; and also 

 the character of the lightning — whether zigzag, ramified, or direct ; also 

 its direction — whether from cloud to cloud, or from a cloud to the earth. 

 Optical phenomena. — Mirage should always be noted, as it serves to 

 indicate the position of strata of greater or less density, which may be 

 produced by open water, as in the case of lateral mirage, or by a cur- 

 rent of wind or warmer air along the surface. 



The polarization of the light of the sky can be observed by means of 

 a polariscoi>e, consisting of a plate of tourmaline with a slice of Ice- 

 land spar, or a crystal of niter cut at right angles to its optical axis, on 

 the side farthest from the eye. With this simple instrument the fact 

 of polarization is readily detected, as well as the plane in which it is 

 exhibited. 



Halos, parhelia, corona?, luminous arches, and glories should all be 

 noted, both as to time of appearance and any peculiarity of condition 

 of the atmosphere. Some of these phenomena have been seen on the 

 surface of the ice by the reflection of the sun's beams, from a surface 

 on which crystals had been formed by the freezing of a fog simultane- 

 ously with a similar appearance in the sky, the former being a continu- 

 ation, as it W'Cre, and not a reflection of the latter. 



In the latitude of Washington, immediately after the sun has sunk 

 below the western horizon, there frequently appear faint i)arallel bands 

 of colors just above the eastern horizon, which may very possibly be 

 due to the dispersion of the light by the convex form of the atmosphere, 

 and also, at some times, slightly colored beams crossing the heavens 



