446 



EEPOET — 1881. 



he obtained. The separation in our case does not produce any marked 

 influence on the final curves, the general featui'es of diurnal and annual 

 changes being virtually identical in both. 



The mean diurnal curve for 18S0 closely follows Professor Everett's, 

 indicating a minimum tension of about 74 volts at 3 p.m., and rising to a 

 maximum of 113 volts at 9 and 10 p.m., from which there is a steady fall 

 to a second minimum of 74 volts at 4 A.M., afterwards rising to the other 

 maximum of 88 volts at 9 a.m. 



In both cases the very rapid fall of tension observed by Birt to take 

 place between 10 p.m. and midnight disappears in favour of a more gentle 

 descent. The difference between the diurnal and nocturnal minimum 

 tensions so conspicuous in the periodical eye-observations also disappears 

 in the continuous records. 



Table III. — Values of Electrical Tension distributed according to 



Wind-direction. 



As regards the curve of annual variation of tension, we find that for 

 1880 the curve more closely resembled that of 1845-7 than it did that 

 of 1863. The months of maximum mean tension were January, when it 

 was 143 volts, and March 136 ; and of minimum, August 37 volts, and 

 September 47 volts. 



Mr. Birt also found the minimum took place in August, but the 

 maximum in January and February. 



Professor Everett gave maxima in November and December, and 

 minima in May and July, with a second minimum in January. 



The curves of diurnal range for each month have also been contrasted, 



