1904. No. 2. THE DIURNAL VARIATION OF TERRESTRIAL MAGNETISM. 3 I 



As the hours for jV = o do not differ more than at the most 04 

 hour, ^6°, from the mean, ir6, I have let the vakies found of t apply 

 to 4 points on the same meridian. 



I must here, however, remark that the angle z for the parallel of 

 Menna does not agree with the others: it is evidendy too small, which 

 may possibly be accounted for by the fact that the scale value for the 

 vertical variometer in Vienna is taken too low. In the »Jahrbücher der 

 K. K. Central Anstalt für ^Meteorologie und Erdmagnetismus«, Jahrg. 1883, 

 p. 226, it is stated that i mm. = 5*70/; but there must have been some- 

 thing wrong with this apparatus, as the instrument appears to have been 

 entirely re-adjusted in Juh^, 1883. For this part of my investigation I 

 have therefore left \^ienna out of consideration, while it is not necessar\' 

 to do so for the calculations on p. 29, as the hour for jZ=o is not af- 

 fected by the scale value. 



I have employed the observations from the other 3 stations in the 

 two following combinations: Pawlowsk -|- Zi-Ka-Wei, and Pawlowsk -j- 

 Tiflis. The combination Tiflis -|- Zi-Ka-Wei is of no use for this purpose, 

 as the lines of direction from the point in question on the parallels of 

 these two stations, to the current, intersect at a very acute angle. 



The values of ip and /i for the point M, calculated by formula (3), 

 are as follows : 



ip h Weight 



Pawlowsk + Zi-Ka-Wei 62° 11' 750 km. 2 



Pawlowsk + Tiflis 61° 27' 1060 » i 



Mean 61° 56' 853 km. 



I have given only half the weight to the combination Pawlowsk -|- 

 Tiflis, as the hour for z/y=o at Tiflis differs so considerably from the 

 corresponding hour at the two other stations. 



Thus according to the above calculation, the part of the current set- 

 ting from E to W should pass, shortly before noon, through the zenith 

 of a place situated only 2° north of Pawlowsk. This, too, accords well 

 with Fig. 2, according to which, as already mentioned on p. 2 1 , the deflec- 

 ting force A for Pawlowsk is seen to have a noon-maxium which remains 

 regularly constant for a couple ol hours, while for the stations to the north 



