70 Lovering and Bond on Magnetic Observations at Cambridge. 
be general and impartial. Until this is done we cannot expect that 
the theory, however complete in itself, will give correct expressions 
of the elements for all parts of the earth. Thus we explain the 
large difference between the calculated and observed declination for 
Cambridge and a few other places. We must however never lose 
sight of the fact that remarkable local disturbances may sometimes 
derange the observed value of the element so as to leave still a few 
cases of unusual discrepance. Part VII. of the “Scientific Me- 
moirs,” contains maps of the lines of declination and inclination on 
the globe for 1838, drawn by Gauss according to his theory. In 
Silliman’s American Journal, No. 2 of 1838, is a Chart of Profes- 
sor Loomis which presents both these classes of lines as they cross- 
ed the United States in 1840; they were projected from a collec- 
tion of all the observations that had been made in the country, after 
they were reduced to the same time. A comparison of the observed 
and empirical lines exhibits sufficient agreement to satisfy us of the 
general correctness of Gauss’ theory in its application to this West- 
ern Continent. Mr. Loomis remarks, in a paper published in the 
Philosophical Transactions of Philadelphia,* that the same dip is 
found in a higher latitude in the western than in the eastern states. 
By recurring to Gauss’ Map of the lines of inclination we notice the 
same singularity in the empirical lines. So also on Gauss’ Map of 
declination, the lines which are far apart in Europe are convergent 
in the northern states as they approach the Magnetic Pole. We can 
readily conceive therefore that an error in the value of the coeffi- 
cients, which should hardly be felt in one place, may be magnified 
into great importance at the other. We dismiss this interesting dis- 
cussion with the confident hope that the simultaneous and extensive 
* Transactions of the American Philosophical Society. Vol. VII, New 
Series. Part I. Philadelphia. 1840. 
