Variation and Dip of the Magnetic Needle. AT 
The general conclusions at which I arrived in my former paper, 
are abundantly confirmed by the preceding observations. They 
all indicate a retrograde motion of the needle, which commenced 
every where as early as 1819, and in some places perhaps as early 
as 1793. The present annual change of variation is about two 
minutes for the southern states ; four minutes for the middle and 
western states; and six minutes for the New England states. 
The observations of variation contained in my present and for- 
mer catalogues were now all reduced to the year 1840, by apply- 
ing a correction for the annual motion, and the lines of equal 
variation laid down upon the accompanying chart so as best to 
represent the observations. It is believed that the errors of the 
chart as thus corrected must be quite small. In my former paper, 
I noticed three observations which exhibited a remarkable dis- 
cordance with the rest. ‘They were for Hanover, N. H., Mont- 
pelier, Vt., and Princeton, N. J. It is gratifying to find that the 
present variation at the former place, as observed by Prof. Young, 
agrees almost exactly with my chart. It is believed that the ob- 
servations at the other two places will be found to be erroneous, 
or that they were affected by very strong local attraction. 
It seems almost superfluous to remark, that most of the obser- 
vations in the preceding table were evidently made with inferior 
instruments, and can lay but a moderate claim to accuracy. A 
large part of the observations are clearly erroneous to the amount 
of half a degree; and the errors of many exceed one degree. 
As most of the errors however are such as may be expected to 
disappear in taking a mean, considerable confidence is placed in 
the position of the lines of equal variation as projected on the 
accompanying chart. ‘To attain materially greater accuracy, ob> 
servations must be made with better instruments and by more 
skillful observers. 
Il. Dip of the Magnetic Needle. 
The chief additional observations of the magnetic dip which 
I have been able to obtain, were made by Prof. Locke and my- 
self... The former were communicated to me by letter; the latter 
are given at large in volume seventh (N. S.) of the Transactions 
of the American Philosophical Society. 
