( 316 ) 



2. The material chosen for this inquirj^ consists of: 



1st. monthly means of barometric pressure at Helder, calculated 

 for the 60 years period Aug. 1843 to July 1902, the total number 

 being 720. 



2"*^. monthly means of barometric pressure at Batavia for 37 years, 

 1866-1902, altogether 444 data. 



3"l monthly means of atmospheric temperature for the whole of 

 France during the 50 years period 1851—1900, altogether 600 data. 



Up to 1873 the data for Helder have been taken from a meteor- 

 ological journal kept by Mr. Van der Sterr and, after his death, 

 from the annals issued by the K. Met. Instituut. 



A Newman standard-barometer at Helder, which is known to have 

 been in use as early as 1851, has recently been tested and does 

 not show any appreciable errors, so that it may safely be assumed 

 that also the records of the station-barometer are sufliciently accurate 

 for our purpose. 



The monthly means for Batavia have been taken from the returns 

 published by the K. Magn. en Met. Observ., and those for France 

 from Angot's "Etudes sur Ie climat de la France, Temperature," 

 published in the Ann. du Bureau Central Meteor, de France, Année, 

 1900, I. Mémoires, Paris, 1902, p. 34—118. 



Table I gives the results of the calculations for Helder. 



Let e be the deviations of the individual data from the cor- 

 responding general average value and n the number of data available, 

 then: 



i /~\^ 

 if = / - — - , mean deviation, 



K n — 1 



i9- = — , average deviation, 



71 



h = . factor of steadiness, 



M\/2 ■ 



li z= — — , idem. 



A = number of years required to obtain a general mean value 

 with a probable error of ± 0.1 mm. for the barometric height and 

 of ± OM C. for the atmospheric temperature. 



This number, calculated from the formula: 



0.6745 M 



is given instead of the probable error of the result with a view of 

 showing how difficult, if not how impossible, it is to fix normal 



