( 557 ) 

 Hh 



(1) 



VW — h' 



By the following reasoning the second problem may also be easily 

 solved. 



The total mean \aliie for a given month, as calculated from n 

 monthly means, must be the same as that deduced from N cor- 

 responding daily means. 



The mean error (incertitude) of the total mean is, as monthly 

 means may be considered to be independent of each other: 



\/-, 



11 {n — 1) yn 



For the mean incertitude deduced in the same manner from 

 observations made three times each day ; 



El. 



too small a value would be found as these observations are certainly 

 not independent of each other; therefore, if the number of obser- 

 vations which, on the average, constitute an independent group be 

 called p, we must have : 



\/n \/N 



If we wish to express the average duration of a disturbance D 

 in numlters of days, we have, in our case : 



.1/,^ A' /,' N 



l) = -±- . — r= — . — (2) 



M;' 3n IP 3« ^ ' 



Table VI shows the values of the interior variability A, thus 

 calculated by means of form. (I) and the duration /J of a barometric 

 disturbance. 



It appears from these results that, on the average, the duration 

 of a barometric disturbance at Helder is in : 



Winter 6.90 days 



Summer 4.89 ,, 



Spring-Autumn 6.04 ,, 



or in round numbers resp. 7, 6 and 5 days in winter, spring- 

 autumn and summer. 



3. It w'oulil perhaps not be iuipossil)le, and it certainly must be 



