NIPHER MAGNETIC OBSERVATIONS IN MISSOURI, 1S7S. S5 



tures, was determined on returning to St. Louis, care being taken 

 to keep the magnet in order during the trip. 



The constant q was determined by the Coast Survey in 1856, 

 and was given by Mr. Schott as o-ooo^o- He stated that this 

 value was rather large, and it was redetermined as shown here- 

 after, the resulting value being o. 4 8 • This magnet is cracked 

 on one side. 



When the instruments were sent from Washington, the two 

 magnets Cg and Cj^ were packed in the declinometer box with 

 the north poles down, the distances between their centres being 

 two inches. In our determinations at Iowa City, it was found 

 that the two magnets, thus placed, acted upon each other in such 

 a way that the value of ni changed greatly for every jar which 

 the box might receive. Each magnet mutually weakened the 

 other, and many irregular changes occurred: As it had been our 

 intention to make only relative determinations of intensity, our 

 work prior to that time was worthless, no deflections having 

 been taken. 



The two magnets were afterwards carried as follows : — The 

 magnet was placed in a chamois case fitting it closely, and was 

 then placed in the metal box ; this box was then slipped into a 

 similar case of leather, so arranged that it could be slung over 

 the shoulder. 



The magnets were always carried, south end up, on the per- 

 son — never allowed to come too near each other ; and in the cars 

 were hung from the roof in such a way that tl>ey could not swing 

 so as to receive a jar. 



The value of m was least during the first week of our work, 

 and thereafter was sensibly constant, showing however a slight 

 increase even then. This increase is caused by the large values 

 of m at Kansas City and Sedalia on the 4th and 7th of Septem- 

 ber, and these observations were made with extreme care. 



The dimensions of the inertia ring j, given by Mr. Schott, 

 are 



Inner radius i.iViS in* ) .. z' o -r- 

 Outer " 1-4215 "• S 



The weight given by Mr. Schott was Si 3.40 grains. 

 Two weighings, on different balances, with different sets of 

 weights (Becker's), gave me 



