Variation and Dip of the Magnetic Needle. 2^1 



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 to a much greater extent than has been hitherto done. 

 And it is 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 mdividuals 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 sufficient 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 

 pubhc 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 : 

 " In 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- 

 riation of the magnetic needle was here 14° W. Proceeding due 

 north to latitude 48° V 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' ; 



