398 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 16 



Swiftsure Bank was sufficiently large in some cases to change the direction 

 of the current brought about by winds of moderate velocity from the char- 

 acteristic deviation of 20 degrees to the right of the wind direction. But with 

 increasing wind velocity the direction of the current approximated toward 

 the direction of 20 degrees to the right of the wind. 



This paper, which was illustrated by lantern slides, will form part of a 

 Special Publication of the Coast and Geodetic Survey, dealing with currents 

 on the Pacific Coast, to be published in the near future. It was discussed by 

 Messrs. LittlehalES, Faris, White, William Bowie, and Humphreys. 



The second paper, on New results concerning the diurnal variation of atmos- 

 pheric electricity, was presented by Mr. S. J. Mauchly, and was illustrated. 



It has long been known that for any given locality the electrical potential 

 difference between the ground and a point in the air, say 1 meter above ground 

 (potential gradient), varies throughout the course of the day in an approxi- 

 mately cyclical manner; also that the amount and nature of this variation is 

 not the same for all localities ; that some localities have two maxima and two 

 minima during a 24-hour cycle while others have only a single "wave." 

 Although various authorities have assumed that the occurrence of the princi- 

 pal minimum about 4 p.m. was a rather general characteristic for nearly all 

 stations, Mache and Schweidler^ long ago pointed out that the phase angle 

 of the 24-hour wave varied greatly from station to station while the phase 

 angle of the 12-hour wave was approximately the same for nearly all the 

 stations. The results of the observations made aboard the Carnegie since 

 1915, representing about half the Earth's surface, indicate that the average 

 diurnal variation of the potential gradient at sea is of the single-wave type, 

 i.e., most days show only one maximum and minimum. However, a much 

 more significant fact is the indication that the time of maximum, or of mini- 

 mum, is approximately the same over all the different oceans, occurring on a 

 universal rather than local-time basis. 



Observations for the diurnal variation of the number of positive ions in the 

 air, and also those for the variation of the electrical conductivity of the air 

 due to its positive ions, indicate that in general both these quantities are, 

 over all oceans, above average value during the day and below average value 

 during the night. But in both cases the average range found was of the order 

 of only 10 per cent of the respective mean values, while for the potential 

 gradient the average range was between 30 and 40 per cent of the mean 

 value. Thus it turns out, on the basis of the Carnegie diurnal-variation data 

 now available, that the computed vertical current density due to positive 

 ions (and probably the total current density) is also subject to a diurnal varia- 

 tion in which a single wave predominates, whose chief maximum (or mini- 

 mum) occurs approximately at the same universal time over all the ocean 

 areas. 



Attention was directed to the fact that the diurnal-variation curves for 

 the potential-gradient derived from the Carnegie observations are very similar 

 to curves which represent the relative frequencies of the aurora borealis as 

 observed at several stations and also to curves representing the diurnal dis- 

 tribution of magnetic disturbances when all are referred to the same time 

 basis. It was pointed out that owing to the non-coincidence of the Earth's 

 magnetic axis with its axis of rotation, the time of daily potential-gradient 

 maximum, as indicated by the ocean curves, corresponds approximately to 



' H. Mach^ and K. v. SchwEidlER. Die Atmosphdrische Electrizitdl, p. 27 (Braunsch- 

 weig, 1909). 



