NIPHER— 4"^ ANN. REP. MAGNETIC SURVEY OF MISSOURI. 469 



The value of Ak turns out to be practically the same as in 187S, 

 as was to have been expected. The value of log. k for any given 

 temperature is less than in 1878 by an amount which would be 

 accounted for by the removal of about 50 milHgrammes (25 mgrs. 

 from each side) from points distant o. j foot from the axis of rota- 

 tion, this being approximately the radius of gyration. Unfortu- 

 nately the magnet had not been weighed, so that this check has 

 not the same value that it might have had.* It is thought, how- 

 ever, that most of this difference is accounted for by the loss in 

 mass of the magnet and the wear of the stirrup. The work of 

 the present year, and of all previous years, has therefore been re- 

 duced by means of the tables of 187S, while in subsequent work 

 the value of log. k^ will be obtained from the preceding table. 



Intensity Determinations. 



During the summer eleven complete determinations of intensity 

 were made at regular intervals. These observations serve to de- 

 termine the value of F in the equation for the deflection series, 

 and lead to a determination of the magnetic moment of Cg for the 

 summer. The other determinations of intensity were relative and 

 were reduced to absolute value by calculating the magnetic mo- 

 ment for the respective days of observation, from the formula which 

 represents the value of the magnetic moment for the summer. 



These calculations are given in the following tables. 



* April 17, 18S2, magnet Cq weighed :03.6c7 grammes. 



