NIPHER MAGNETIC DETERMI VATIONS IN MISSOURI, 79. I35 



Declifiation. 



The following tables give the calculations for the work of the 

 summer. In most cases the mark reading in the first table is the 

 mean of readings taken in the evening before the observation, 

 and in the morning after the observation. The reading of the two 

 verniers are always taken, the degrees being always from A. 



The azimuth of the mark, as given in the 7th column, is esti- 

 mated from the S. and from the station where the star observation 

 was made. In the last column, the azimuth from the declination 

 station is given. This is deduced from the previous azimuth by 

 determining at each station the angle between the mark and the 

 other station. These angles were repeated five times. This plan 

 was adopted in order to get a morning reading of the mark. It 

 was, of course, necessary to make the star observations at some 

 point where the transit could be left in safety, and such points 

 were not always suitable for magnetic determinations. 



The following is a reduction of the three observations on thesun : 



Station. 



Glasgow 



Kansas City . 

 Schell City . . 



Date. 



July 21 



" 29 



Aug. 25 



a.c.log.co8^ 



O.I 1087 

 o. 1 1024 



0.10372 



Cor. I South. 



Mark. 



Az. of Mark. 



-1-2.9' 90° 33'. 4 i8o°co'.2 89°26'.8W. 

 4-3-2 132 40 .7|i79 16 .446 35 .7 W. 

 -I-2.414S 41 .5180 00 .5[3i 19 .oW. 



In the table, / represents half the sidereal interval between the 

 morning and afternoon series, and J4 (^A-\- A'^ is the uncor- 

 rected reading of south. Treating this quantity as constant, the 

 probable error of the mean of the n observations is given in col- 

 umn e. The correction due to the change of solar declination is 

 given in a succeeding coluhin. 



The formula by which this reduction is made is given in the 

 former report. (See p. 83.)* 



* See Chauvenet, Pract. Ast. I., p. 432. 



