G8G 



EXPEDITION TO POINT BARROW, ALASKA. 



On September 26 there was quite a disturbance of the needle five hours in advance of the 

 aurorii. Just after the appearance of the aurora the current began to weaken and shifted from 

 north to northwest. 



On September 26 there was an increased current one hour in advance of the aurora. 



On October 8 a westerly current changed to a little south of west one hour in advance of the 

 aurora. 



At other times auroras occurred when there was a strong or moderately strong current without 

 apparently having the slightest effect. 



NOTE ON AN IMPROVED METHOD FOB OBSERVING GROUND CURRENTS. 



Heretofore the best method for observing ground currents has been that of two lines, one in 

 the magnetic meridan and one at right angles to it. By this method the difference of potential 

 between N. and S. and between E. and W. giving the components of the current in these two direc- 

 tions can be obtained. This, however, is not sufficient to enable us to determine the exact direc- 

 tion and strength of the current. 



Now, if the difference of potential between N. and W. is taken at the same time as that of N. 

 and 8. and of E. and N., there will be all the necessary data to plat the eqnipotential surfaces, 

 from which the direction of the current can be obtained. 



Then, knowing distance between the equipotential surfaces, we can get the variation of the 

 potential with respect to the distance and hence the strength of the current. 



The lines need not be at right angles, nor is it necessary that one should be in the magnetic 

 meridian. 



II. THICKNESS OF THE ICE. 



The thickness of the ice in the lagoon close to the station, and in the still water of the sea 

 near shore, was measured at intervals of about a month during the winter. 

 The following table presents the results of these observations : 



NOTE. In the meteorological observations, the readings of the barometer are iiot reduced to 

 the .sea-level. 



