NIPHER 4^'^ ANN. REP. MAGNETIC SURVEY' OF MISSOURI. 465 



The angle of deflection at the lower temperature was determined 

 from the simultaneous readings before and after the experiments as 



is here shown: Series I. .Series III. 



No. 1 read 77. ^^ 78.9. 



Mean of day 78.7 78.7 



Correction to mean -j- o.. 



■26 



Reduced to scale value of C, 7 — o.^g -j- o.^g 



Ci7 '■ead 79-0 79-35 



Ci, corrected 78.,! 79.^^ 



C J - during deflection 151-25 iS^-ee 



Angle of deflection in scale div 'j2.,j^di\. 72.^5 div. 



Hence the mean angle u at the lower temperature /^ is 72.^^ div. 

 or 3° 29'.4. 



Using the notation, 



s = scale value of C^^ ( ^ ^.'gg), 



u = deflection at lower temperature ( ^ 3° 2^'.^), 



I = length of I' in units of radius, 



d =1 change in scale reading of Cj^ (1-42)^ 



for change (/ — /„) in temperature of (Cg), where 



^-^o = 37°-,5F. 



„,, s. d. 1. 

 I hen (7 := . cot u . 



Substituting the known values, we have 



^ ^ °-00047 - 



In 1879 the result was 



? = °-00048 • t 



The result indicates that the determination of 1879 i^ satisfactory, 

 and the table of temperature corrections then deduced and given on 

 p. 90 {/oc. cit.) based on the value o.^QQ^g has been used in redu- 

 cing the observations of the present report. 



After this determination the deflecting magnet Cg was, through a 

 misunderstanding, left in the cool air-bath and the next morning it 

 was found to have oxidized. This made it important to redeter- 

 mine the moment of inertia as function of temperature. 



A series of determinations beginning October 18, 1S81, and closing 

 Mar. 29, 1882, was therefore made, the experiments being conducted 



* Trans, vol. iv. No. i, pp. 88-90. 



