3 I2 



SCIENTIFIC RESULTS OF ZIEGLER POLAR EXPEDITION 



SECULAR CHANGE IN MAGNETIC INCLINATION 



Observations were made for inclination, as noted in the tabulation of dip results, at the 

 Italian magnetic station of 1899 and 1900. In order to have the resulting values apply to the 

 same mean time at both stations observations were first made at the Italian station with one 

 polarity of the marked end of each needle ; the instrument was then transferred to pier D in 

 the observing hut, where complete sets with each needle were made, and finally the comparison 

 was completed by observing with second polarity of the marked end of each needle at the Italian 

 station. Assuming a linear change in diurnal variation over the period of observation, the 

 mean results at the two stations are directly comparable. The mean resulting difference in 

 magnetic dip between the two locations is 7/3 as adopted from the following tabulation of the 

 comparisons : 



The comparison of June 6 is given weight of one against two for each of the other com- 

 parisons by reason of the observer's note regarding discovery of iron bolt at foot of pier on 

 June 20. There being no reason to assume any change in local magnetic conditions at so 

 isolated and unfrequented a locality, we may assume the same difference at the time of the 

 Italian Expedition. 



Commander Cagni's observations resulted as follows :* 



D a t e Number of de- Mean observed 



terminations inclination 



August 21, 22, 1899 4 83 25/0 N 



July 10, 16, 17, 23, 1900 9 83 01.2 



whence the mean value 83 13/1 N for the epoch 1900.09. Referred to the Ziegler Polar 

 Expedition station, this becomes 83 13/1 4- 7/3 = 83 20/4. The value for the epoch 

 1904.13, as above, is 83 12/4 N. Both of these series are uncorrected for diurnal variation. 

 Each, however, consists of observations made at various parts of the day, so that the means 

 may be assumed as applying practically to mean of day at their respective epochs. Thus in 

 four years the northerly magnetic inclination in the region of Teplitz Bay has decreased 8'. 

 Hence the rate of change in magnetic inclination due to secular variation, assuming this effect 

 to be a linear function during the elapsed interval, is 



2' per year. 



This value is, while of the same sign, considerably smaller than that taken by Professor 

 Palazzo as a result of his discussion of Commander Cagni's observations, viz. , 24'. He, 

 however, considers this determination as not very reliable, owing to the short period between 

 the inclination observations, and also the great variation between the individual values obtained. 



* Osservazioni scientifiche esequite durante la spedizione Polare di S. A. R. Luigi Atnedeo di Savoia, Duca 

 degli Abruzzi, 1899-1900. Milan, 1903. Pp. 462-475. (Relazione sulle osservazioni magnetiche fatta dal Pro- 

 fessore Luigi Palazzo.) 



