NIPHhR MAGNETIC DETERMINATIONS IN MISSOURI, '79. I33 



lyd^ o. 



Hence the values 



log. Wo = 9- 



[a^J 7007 



and 



log. m = 9.37000-0 000020 ^• 



In order to determine the corrections to be applied to the 

 determinations of intensity in 1878 and 1879, in order to elimi- 

 nate the effect of the magnetic brass-work of the instruments, the 

 following experiments were made in the physical laboratory of 

 the University. 



1. Declinometer No. 3 was relieved of all brass connected with 

 it, and magnet Cg was oscillated to determine the value of m//^ 

 the value w being assumed constant. The scale was illuminated 

 by the reflection of the northern sky from a distant plane mirror. 

 All iron in the room was, of course, left undisturbed. 



The laboratory being on the third floor, the vibrations of the 

 building made it impossible to secure as good results as might be 

 desired, and the lack of time for systematic work made it impos- 

 sible to conduct the experiments elsewhere. 



2. The same magnet was oscillated in the magnetometers of 

 1878 and 1879. 



Each determination was corrected for torsion, and was reduced 

 to the mean temperature of the series. 

 In the following tables, 



7/ = the corrected value, or the intensity of the field when 



uninfluenced by the brass-work. 

 //' z= the horizontal intensity with the magnetometer ol 



1878. 

 //'' z= the same with the instrument of 1879. 



A preliminary determination made October 25th gave the fol 

 lowing result : 



log. m//= 0.5 10 16 ' log. m//' == 0.50903 ; 

 hence //= (1+ 0.0026) ^' • 



It became necessary to make some changes which altered 

 the value of ^, and on November loth a new series was begun. 



In the following table («) are numbers which indicate the or- 

 der in which the determinations were made. As will be observed, 



