( 19 ) 



as a surrogate, flie atitlior siifin-csts tlie repeated rearrangement of 

 the records accordiiiu' to difïerent periods, iiol iiiiich differinf»; from 

 the period in question. Thus, in a purely empirical way ("by trial"), 

 a standard may be obtained by whicli a correct estimate can be 

 formed in how far tlie ontcome arrived at must be considered as 

 a merely accidental one. 



Now the same problem was treated some 15 years ago ') by the 

 author of this paper after a different metiiod, applied not only to 

 magnetical but as well to meteorological data of different description, 

 and Prof. Schuster's important investigation gives a ready occasion 

 for taking this pi'oblem in hand again. 



It is only natural to choose in the first place for this iiupiiry the 

 series of barometric observations made at Batavia which now extends 

 over a period of 3fi years (186t) — 1901). 



An investigation into a possible synchronism between the frequency 

 of sunspots and atmospheric temperature, commenced in 1873 "*) and 

 recently conducted up to date ^), gives some ground to the expectation 

 that, for inquiries of this kind, observations made at tropical stations 

 are of more value than those made in regions where the atmospheric 

 disturbances are such as experienced in higher latitudes. 



In the second place it seems desirable to look for a shorter way 

 for coming to a reliable criterion than the tedious process of the 

 calculation of Schuster's periodograph. 



2. An arrangement of quantities according to a given period T 

 may be executed by measuring out the successive data from a point 

 () taken as origin and along straight lines drawn through this point 



2-r 



at equal angular distances -— . 



If we assume the unity of mass attached to the ends of those 

 radii, it is evident that a judgment may be foi'med about the degree 

 of symmetry in the distribution of the masses with respect to point 

 0, by simply calculating the average \'alue of all these vectors, or 

 in other words to determine the situation of the centre of parallel 

 forces supposed acting on the masses. 



If the (piantities T show a well marked periodicity as e.g. tidal 



Ï) Observ. Magn. Meteor. Obsei'v. Batavia. X, 1888, Appeiul. II also Natiiurk. 

 Tijdschr. XLVIII. 1889. 



Vei-h. Kon. Akad. v. Wet. Amsteidani. XXVlll, hSiUi. 



-) Koppen. Zeitsclir. (Jesterr. Gesellscli. f. Meteor. Vlll, 187;). 



•'') C NoRpiMANN. Essai sur le role des ondes Hertziennes and : Astron. Pliys. et 

 sur diverses questions qui s'y rallachent, These, Paris, 1"J03. 



2* 



