ARTICLE XV. 



Observations of the Magnetic Dip in the United States. Fourth Series. By 

 Elias Loomis, Professor of Mathematics and Natural Philosophy in Western 

 Reserve College. Read May 6, 1842. 



Although my dipping needle might be regarded as tolerably well tested by 

 the observations in different azimuths, contained in the Society's Transactions, 

 Vol. VIII., p. 66, still, as this examination was limited to a portion of the axis 

 of each needle, I was disposed to institute another trial. For this purpose I 

 resorted to the method of Mayer, loading the needles with sealing-wax. The 

 following tables exhibit a summary of the observations. Columns second and 

 third show the observed angles with a vertical, when a mark on the face of the 

 needle was turned successively to the east and west; columns fourth and fifth 

 show the same with the polarity reversed. The last column shows the dip 

 deduced by Mayer's formula. 



Needle No. 1. 



Date. 



Poles Direct. 



Poles Reversed. 



Dip DEDtrcED. 



Mark East. 



Mark West. 



Mark West. 



Mark East. 



1841, April 



27, 8— 9, A. M. 



17° 8'.4 



+ 17° 17'.9 



17° 



22'. 3 



+ 16° 



56'. 6 



72° 48'.7 



May 



13, 7— 8, A. M. 



39 27.8 



— 9 57.9 



37 



48.9 



— 10 



12.0 



44.5 



May 



15, 7—12, A. M. 



41 39.5 



— 13 22 .5 



38 



11 .3 



— 10 



44.0 



42.7 





(1 (( li 



49 6.6 



— 26 34.9 



45 



54.2 



— 23 



45.8 



44.6 





H (« It 



51 52.0 



— 31 42 .0 



46 



2.7 



— 24 



1 .3 



46.7 





(( (( 1< 



61 28 .3 



— 49 19.7 



56 



1 .2 



— 42 



29.2 



53.2 





(1 11 11 



59 32.6 



— 45 55.2 



56 



20.5 



— 42 



57.1 



51 .9 





" 1— 6, P. M. 



60 23.9 



— 47 25.5 



57 



39.2 



— 45 



22.8 



52.6 





It 11 11 



34 10.6 



— 1 49.4 



39 



25.1 



— 13 



17.8 



42.8 





11 11 It 



27 20.2 



+ 6 41 .8 



27 



25.1 



+ 5 



11 .6 



42.7 





11 11 11 



24 44.4 



-1- 10 18.5 



23 



30.6 



+ 9 



11 .2 



47 .4 



Mean of 12 



11 11 11 



17 11 .1 



+ 17 22 .6 



16 



52.4 



+ 17 



23.3 



47.6 



observations, Neec 



lie No. 1, ( 



960 readings,) 



72° 47'. 1 



