530 



EXPEDITION TO POINT BAEKOW, ALASKA. 



The numbers contained in the last three columns of this table were plotted on the accom- 

 panying diagram, which shows the vertical force to be in excess of its average value in the (local) 

 morning hours maximum about 6 a. m., and in deficiency in the (local) afternoon hours minimum 

 about 9 p. m. Compared with the variation of the vertical force at more southern stations, there 

 appears to be a complete inversion of the hours of greater and of less intensity, which may be due 

 to the action of disturbances; or, if regular, it may be somehow connected with the circumstance 

 that Uglaamie is near the central zone of maximum auroral display, and a little to the north of it. 

 We note the apparent greater range of the diurnal variation iu the half year including the winter 

 than in the other six months, which is also an anomalous phenomenon. 



The breakage of the magnetic and electric equilibrium in this auroral zone, resulting in an 

 outburst of disturbances, probably occurs more frequently in this belt than outside of it, and pos- 

 sibly sudden changes of temperature may be favorable circumstances of disruption. The belt of 

 maximum auroral development seems to be subject to fluctuations in position, and in studying the 

 supposed connection of auroras with terrestrial magnetism, attention should be directed to the di- 

 rection in which the aurora appears at a station, i. e., at Uglaamie, whether to the south or to the 

 north of the zenith. 



The increased dip and total intensity in the Uglaamie morning hours, as contrasted with the 

 diminished dip and intensity of the total force in the afternoon, is corroborated by the observations 

 made in the first year by means of the dip circle and deflecting weight. 



DIUKKAI, \XRIMTOK or -ran MAGNETIC VERTICAL TOTICH 

 Observed af Ck>(*laanrfe ; .Mask* 



INCLUDCDt) 



Solar diurnal variations in the magnetic dip and in the total inagnrtw intensity. 



These viii iations are readily obtained from the variations in the horizontal and in the vertical 

 components of the force; if F= total force, If and 7 its horizontal and vertical components, then 



