Variation and Dip of the Magnetic Needle. 291 
frequently in the accuracy of. the observations, still it is thought 
that its publication may prove useful at least in two respects if in 
no others. First, some do not seem to regard it as settled beyond 
dispute, that the magnetic needle has at present a retrograde move- 
ment compared with its motion the last century. I trust the ob- 
servations I have here brought together, may be considered as fi- 
nally settling this important question. And secondly, it is hoped 
that this article may remind men of science of the importance 
of observations of this kind, and of the need there is of multiply- 
ing them toa much greater extent than has been hitherto done. 
And itis hoped moreover that they will not be content with sim- 
ply making their observations, but that they will see to their pub- 
lication. Probably many individuals who have taken observa- 
tions sufficient to determine the magnetic variation in their re- 
spective places, have deferred publishing them because they did - 
not regard the observations as of suflicient consequence. But al- 
though it is of little importance to the theory of magnetism to be 
informed of the variation of the needle at one place alone, yet 
when like observations are collected from every part of the coun- 
try, their united value is immense. It is hoped then, that who- 
ever has accurate magnetic observations which have not been 
published, will see that they are recorded in this or some other 
public journal. Such a record may be made within the space of 
two or three lines, and if the practice were extensively followed, 
we should have the materials for laying down with considerable 
accuracy the lines of equal variation throughout the United States. 
The substance of the letters which I have received, may be 
gathered from the following observations. Mr. John Johnson, 
Surveyor General for Vermont, thus writes from Burlington : 
“Tn the year 1817 I determined the latitude of the source of the 
St. Croix, 45° 55’ N., and longitude about 67° 55’ W. The va- 
ration of the magnetic needle washere 14° W. Proceeding due 
north to latitude 48° 1’ N. I found the variation 17° 45’ W. In 
1818, near Timiscuata Lake, latitude 47° 38’, longitude about 69° 
W., the variation was 16° 31’. In 1818 at the Matwaska settle- 
ment, on the river St. John, latitude 47° 12’, longitude about 68° 
10’, the variation was 16° 45’ W. 
» “ At the University of Vermont, in Burlington, near where I re- 
side, lat. 44° 28’, long. about 73° 14’, I found in 1818, the varia- 
tion 7° 30’ W. ; in 1822, 7° 42’ W.; 1830, 8° 10’; 1831, 8° 15’; 
