Coast Survey of the United States. 239 
erto, that without it any map or chart would disgrace the office 
from which it issued. ‘To this the superintendent has added 
other results without increase of expense. ‘There is no branch 
of physical science which, at present, engages more active atten- 
tion than magnetism. The magnetic surveys conducted and 
observations established by the government of Great Britain at 
home, and all over the world, are worthy of the munificent sup- 
port that nation has always given to science, and the diffusion of 
sound knowledge. [tis a matter of humble pride that something 
has been done also in this country, at the magnetic observatory 
of Cambridge under the direction of Professor Lovering and Mr. 
Bond, and still more at the observatory of Girard College under 
the direction of Dr. Bache. The publication of the latter obser- 
vations, with the curves of diurnal and monthly variation, by the 
government of the United States, enables this country to adda 
respectable mite to the general contribution. 'The new instru- 
ments invented by Dr. Lloyd and M. Weber, are now used upon 
the survey. 
The portable declinometer of M. Weber, (perfected by Lieut. 
Riddell, and manipulated according to his instructions, ) measures 
inclination, and also, by a subsidiary apparatus, the horizontal 
force, according to the method of Gauss. The bar being vibra- 
ted gives magnetic moment. of bar Xhor. mag. intensity. And 
the same bar used to deflect another suspended at different dis- 
tances, gives a series representing mag. mom. of deflecting 
bar—hor. mag. intensity, and hence the true horizontal force is 
derived. Excellent results have been obtained by Fox’s dip 
circle, with the use of the deflecting magnet. The axis in jew- 
eled holes has a projecting stem, which is rubbed with an ivory 
disk to ensure perfect freedom of suspension. ‘'T'o this happy plan 
of creating aslight motion of the axis, a Frenchman has applied 
the significant term of shuddering. By means of these instru- 
ments the declination, inclination, and intensity, (both horizon- 
tal and vertical,) are determined, and thus whilst the useful and 
necessary are soughi, valuable additions are made to the general 
magnetic researches. 
Local attraction, and the consequent imperfection of courses 
on board of a vessel, will receive the attention their importance 
demands. Experiments made last summer on board of the brig 
Washington, belonging to the coast survey, showed a considera- 
