NIPHER MAGNETIC DETERMINATIONS IN MISSOURI, '8o. 



335 



Station 41 — Gate-wood, Ripley Co., Mo. Lat. 36° 31'. g ; Lon. 91° 

 •03'. 0- N.W. qr. of N.W. qr. of sec. 8, tp. 22, r. i W. of 5th pr. meridian, 

 on the farm of J. F Oneal. The observations were made in the front yard, 

 midway between the house and the fence. The observations were made 

 and reduced precisely as at Doniphan. 



Station 42 a — Piedmont, Wayne Co., Mo. Lat. 37° oS'.^; Lon. 90° 

 41 ' . 4. Station W. of the yard of Dr. Pettit, and 42 ft. from the middle of 

 the garden fence, near the edge of the timber. Complete determinations 

 made here. Meridian by polaris obs. 



While reading the magnet scale in the first declination^ observation, 

 two trees, one no ft., the other 210 ft. distant were simultaneously struck 

 by lightning. A stinging spark passed from the telescope to the obser- 

 ver's head, but the needle was not visibly affected. 



Up to this determination the declination magnet had been suspended 

 on a bundle of silk floss, which had first been rendered permanent by a 

 long suspension of the torsion weight. As it had been necessary to break 

 this fibre at Poplar Bluflfs in order to exchange stirrups, the first Piedmont 

 declination was not very satisfactory, as the newly tied fibre developed 90° 

 of twist during the day. Assuming no error in the morning elongation, 

 this would make a correction of — >]' .^ on the declination. The floss was 

 replaced by a single fibre in all subsequent work. 



Station 42 b — Piedmont. Station 270 ft. nearly due N. of station "a." 

 A check deteimination of declination was made here, the magnetic meri- 

 dian being determined by a single reading of the axis of magnet No. i at 

 3 :35 P.M. The true meridian was deduced from station " rt." 



Station 43 a — Arcadia, Iron Co., Mo. Lat. 37° 46'. 2 ; Lon. 90° 40.8. 

 •Observations in the garden of the hotel, on the walk midway between the 

 spring and the front gate. The triangulation station on Pilot Knob bears 

 N. 3° 42'. y E. In this region local influence is very great, and the best 

 average value for declination is deduced from the determinations of J. 

 Pumpelly and P. N. Moore in 1872. Several hundred determinations gave 

 them 7° 30'. Assuming an annual decrease of 2/, this would give for 1879 

 a declination of 7° 16'. 



A polaris observation was made here, but some unknown error amount- 

 ing to several degrees occurred in the work. The meridian was deduced 

 from observation at the next station, and the result thus obtained was 

 afterwards checked by a polaris observation made about an hour before 

 elongation. 



Station 43 b — base of Pilot Knob, at the N.W. end of the triangulation 

 base line. This station is about at the vertex of an equilateral triangle, 

 the other vertices of which are at the extremities of the N.E. side of the 

 old fort. It is marked by a large limestone rock one foot below the sur- 

 face of the ground. A drill-hole in this rock is filled with lead, in which 

 is cut a cross. From this station, the station on the summit of Pilot Knob 

 bears S. 8i° sS'.g E. A single reading of the magnetic axis was taken at 

 I :49 P.M. of the 19th. 



