NIPHER MAGNETIC DETERMINATIONS IN MISSOURI, 'So. 337 



At the next station the sustaininpf fibre was found to be frayed and in 

 contact with the glass tube. This probably accounts for a very irregular 

 oscillation series which was first made. A second series gave a somewhat 

 better result. The source of the trouble was not discovered at the time. 

 For this station, therefore, the oscillation and deflection series were re- 

 duced independently as relative determinations, and reduced to abso- 

 lute measure by calculating the value of ;« for that day as explained under 

 station 40. 



Station 47 — C«(5«, Crawford Co., Mo. Lat. 38° os'.g ! Lon. 91° 

 2i'.o. Station in the road in front of the schoolhouse and 125 ft. distant. 

 Sun observation for meridian. 



Station 48 a — Salem, Detit Co., Mo. Lat. 37° 39^.0; Lon. 9i°3o'.6. 

 In the meadow of Dr. J. N. McMurtrie, a few yards N, of the barn and just 

 N. of the shallow slough. The S.E. corner of the court-house bears S. 42° 

 59'. 4 W. The meridian was determined by a pole-star observation. As 

 the declination was over half a degree less than was expected, the meridian 

 determination was checked by a sun observation. No error being detected 

 here, observations for magnetic meridian were made at the two following 

 stations. 



Station 48 b — On the hill 420 ft. N.E. of station "a.'' The true meri- 

 dian was deduced from station "a," and the magnetic meridian was deter- 

 mined by a single reading of the axis of Cg at 5 : 20 o'clock p.m. 



Station 48 c — About 500 ft. nearly N. of station " «." Observations 

 made at 5 : 40 p.m. as before. 



The observations all agreed very well, nevertheless it seemed probable 

 that the unexpected result was due to local causes, and not much weight 

 was given to the observations until a conversation with Prof. Emerson, of 

 the RoUa School of Mines, brought out the fact that the declination at 

 Rolla is practically the same as at Salem. This established the existence 

 of the looped area of minimum declination shown on the map, and also 

 explained fully the anomalous result at De Soto. Subsequent determina- 

 tions at Houston were also confirmatory. It is to be remarked that the 

 western iron field in Missouri (which lies chiefly in the triangle whose ver- 

 tices are at Rolla, Cuba, and Salem) is partly coincident with this area of 

 minimum declination. To what extent the iron deposits (chiefly specular 

 ore in sandstone) are the cause of this minimum area, is a question which 

 requires further attention. It should be stated that no iron is known to 

 exist in the immediate vicinity of the stations of observation. 



Station ^g—Housion, Texas Co., Mo. Lat. 37° 19. 2 ; Lon. 91° 55'. 2- 

 This station and the following one were reached by wagon from Salem. 

 Only relative intensity determinations were made here, magnet Cg being 

 oscillated in Declinom. No. 3. The absolute value was calculated as ex- 

 plained under station 40. The observations were made in the front yard 

 of the Texas House, 25 ft. from the W. fence and 68 ft. from the line of the 

 N. side of the house. 



