62 Variation of the Magnetic Needle. 



servation made ,on the 1st August, 1818, shewed it to be 5° 

 45', and on the 24th of the present month of April, ( 1 825) be- 

 tween 9 and 10, A. M. it was exactly 6° 00' ; all which shews 

 that there has been since 1817a retrograde motion of the nee- 

 dle of about two minutes per year — whether this is general 

 or local, I have not had the means of ascertaining. Mr. 

 Joseph Henry, a member of the Institute, surveyed a farm 

 in the town of Coeymans, not many days ago, which had 

 been run by the late John E. Van Alen, one of the best sur- 

 veyors of our country, in 1798, and the variation was found 

 to be one degree, as nearly as could be ascertained, in the 

 same way ; that is, from the north to the west. 



It will be recollected that in 1806, a total eclipse of the 

 sun of uncommon duration, took its range over our country. 

 May I be permitted to escape the charge of advancing in 

 absurdity, in suggesting the possibility that the lunar effluvia 

 conveyed to the earth by the rays of the sun, on that occa- 

 sion, might have had an agency in producing the phenom- 

 enon I have described.* Be that as it may, there appears 

 to be something remarkable in the coincidence of these oc- 

 currences. 



^ In a Memoir which I had the honor of reading before the Institute some 

 time since, on " the Functions of the Moon," which will probably appear in 

 some future publication of our Transactions, I have extended my remarks in 

 relation to the probability, that the eclipse of 1806, had an effect on the polar- 

 ity of the magnetic needle. 



