DISCUSSION OF BAROMETRIC OBSERVATIONS. 



465 



of this atmospheric disturbance in every part of the year, as well as a 

 more accurate account of the annual fluctuation of pressure, the daily 

 means of the barometer for the twenty-five years were next arranged 

 under each day of the year in two columns, one column containing 

 those means which exceed the normal value for the i^articular day in 

 question, derived from Table I, the other column containing the means 

 for like-named days in the remaining years, all falling below the com- 

 puted normal value. Each column having been added, the diflerence 

 between its sum and the product of the normal value by the number of 

 means in that column was found. Then if d and d' represent these differ- 

 ences, N the normal value, and n the number of means in both columns 



taken together, (twenty-five, except when an omission occurred,) — l!^— 



is the onean of the departures of the daily means from the normal value for 



d—d' 1 



that dav of the year, and N4- 1 equal to th of the sum of the two 



71 n 



columns, is the mean pressure for the same day. The mean pressures for 



every day of the year, thus deduced, are as follows : 



Table II, 



As might be expected in so short a series as twenty-five years, the 

 values embraced in this table are far from escainng the effect of acci- 

 S. Mis. 31 30 



