14 



Prof. Everett Observations of 



[Jan, 



results agree very well with those derived from the previous six months, 

 allowing for the difference between the length of the day in summer and in 

 winter. 



The following Tahle of the variations of electricity in fine weather, from 

 month to month, embraces the whole period of observation down to Febru- 

 ary 18G4. These results, as well as those above given, are expressed in 

 units of station electrometer with second fibre, being the same unit that 

 was employed in the previous paper. 



The day is supposed to be divided into three portions before noon, 

 noon to 6 P.M., and after 6 P.M. For each month, all the observations in 

 each portion have been summed and divided by their number, giving the 

 means shown below. 



a. Second fibre put in December 6th. 



b. Third fibre put in July 3 1st. 



c. The electricity on February 17th and part of 18th was out of range, and has not 



been reckoned. 



Tbese results show that atmospheric electricity is stronger in winter than 

 in summer, and seem to indicate a double maximum and minimum within 

 the year, the principal maximum occurring about February, and the other 

 maximum about October ; the principal minimum in June, and the other 

 in November. It will be observed that in every case the numbers in the 

 column " after 6 P.M." are the smallest. 



At the suggestion of Professor Thomson, I have made a careful compa- 

 rison of the states of electricity, as regards both strength and variableness, 

 for different directions of wind. For this purpose I have tabulated accord- 

 ing to direction of wind (separating also fine-weather from wet-weather 

 observations) the daily entries of mean potential at 2 P.M. for the first 

 twelve months, also the variableness as measured by the difference between 

 the entries of highest and lowest potential for the same hour. Where 

 there was no observation between 3 and 4 P.M. the day was passed over ; 



