134 



TRANS. ST. LOUIS ACAD. SCIENCE. 



they were so arranged as to detect any change in the value of H 

 during the series. 



Hence for the correction of the series of 1878,* 



/r== (I + 0.0029)^'; 



and for the vakies of 1879, 



Hz=: (l _ 0.^070) J^"- 

 In 1879, at Iowa City, Decl. No. 3 of the Coast Survey was- 

 used, with the new leveling screw. A similar series with the 

 instrument thus arranged gave on November 17, 

 7nH- . 



3-389 

 3-384 

 3-388 



Mean, 3.397 



Hence, H= (i+o-oore) ^" • 



It will be observed that while the lower end of the north level- 

 ing screw of D. No. 3 is much more strongly m.agnetic than any 

 other part of the brass-work, nevertheless its effect as a whole is 

 less than that of the two south screws. Hence the replacing of 

 the original north screw by a purer one has increased the numeri- 

 cal value of the correction. These corrected values of ^ will all 

 be tabulated at the close of the final report in 1880. 

 Inclination. 



The determinations were made with the instrument described 

 in the former report, and in the same manner. 



