lo SCIENTIFIC RESULTS OF ZIEGLER POLAR EXPEDITION 



(6) After removal of tacks, by W. F. Wallis : 



Mean 



20068 



Observations by Magnetometer No. 26 gave the following results : 



Date 

 1905 



September 

 October 



Mean 



Horizontal 

 intensity 



r 

 20057 



65 



20061 



Consequently values of horizontal intensity determined with Magnetometer No. IIII 

 before the removal of the tacks must be increased by about 250 r- 



The presence of tacks would affect only the oscillations, since throughout deflections the 

 suspended magnet and the tacks would be always in the same relative position. Instead of 

 the ordinary formulae, use should be made of the following to reduce observations of horizontal 

 intensity made when the tacks were present : 



T' 



H 



and — =: 



m sm 



From the observations at Cheltenham in 1905, J^fwas found to be very nearly —500;'. 

 The application of this correction to the Teplitz Bay and Alger Island observations has been 

 made as follows : The combination of the above equations in the usual way to eliminate m 

 gives the value of V H{H-\- X), from which H may be derived when X is known. At Tep- 

 litz Bay the average value of V H{H + X)was65io;', from which ^=6765;', lor X= —^ooy, 

 or H= V H {H -{- X) -\- 255^. The same correction applies for Alger Island. 



The last column in the following table gives the mean value of log m reduced to 20° Cen- 

 tigrade for various groups of observations and furnishes the means for comparing the magnetic 

 moment of the intensity magnet at Teplitz Bay and Alger Island and in the United States : 



