Variation and Dip of the Magnetic Needle. 41 



Art. V. — On the Variation and Dip of the Magnetic Needle in 

 the United States; by Elias Loomis, Professor of Mathemat- 

 ics and Natural Philosophy in Western Reserve College. 



Communicated to the Conn. Acad, of Arts and Sciences, and read April 28, 1840. 



I. Variation of the Magnetic Needle. 



In the number of this Journal for July, 1838, (Vol. xxxiv,) I 

 have given a collection of all the observations on the variation of 

 the magnetic needle in the United States, which I had at that 

 time been able to collect, and from them was enabled to draw up- 

 on a chart the lines of equal variation with tolerable accuracy. 

 The observations, however, exhibited various anomalies, and 

 for the southern part of the country were very few in number. 

 Further information on the subject was therefore desirable. I 

 have accordingly sought observations from every source in my 

 power; with what success the present article will show. The 

 earliest information on the subject I have been able to obtain, is 

 contained in the Journal of Hudson's third voyage, in 1609, when 

 he discovered Hudson River. The Journal is contained in the 

 third volume of Purchas's Pilgrims, from which the following ex- 

 tract was furnished me by Prof Jared Sparks, of Cambridge. 

 Hudson came to the Grand Bank of Newfoundland, and proceeded 

 along the coast to the thirty-fifth degree of latitude. He does 

 not mention his 'longitude, but was commonly in sight of land. 

 July 3, 1609. Bank of Newfoundland. Lat. 44° varia. 17°w. 



Vol. XXXIX, No, 1. — April-June, 1840. 



