376 P. E. Chase on Terrestrial Magnetism. 
bring the floating strip into a line with the outstretched arm, 
and the tendency may be increased by moving the basin gently 
up and down. 
2. Hold the gimbals of a binnacle compass so that it can 
swing only in one direction, and cause it to move like a pendu- 
Jum in that direction. The needle will tend toward the line of 
oscillation. Vessels may have been lost from ignorance of this 
fact, for it is not unusual for compass pivots to become so worn 
that the needle moves sluggishly, and, in order to start it, the 
compass-box is shaken. If one of the gimbal hinges should be 
rusty, the shaking would bring the needle toward a line perpen- 
dicular to the axis of the free gimbal, and the captain might 
easily suppose that he was sailing rorth, when his course Ww 
due east or west. 
. Take an ordinary pocket compass, grasp it firmly between 
the thumb and finger of one hand, and move it-quickly up and 
down through a small are. The needle, as in the last instance, 
will tend toward the plane of motion. This experiment may 
be variously modified, according to the length and directive en- 
ergy of the needle, the steadiness of the operator’s nerves, &e. 
Sometimes a simple grasp, with a powerful muscular contraction, 
will bring the needle into line, without any other vibration than 
that which arises from the irresistible nervous tremor. Some- 
so rapidly as to become nearly invisible. isd 
The polarity in each of the three cases here enumerated, 18 
different individuals over the needle. me can bring it into 
ine at once, with scarcely any perceptible motion, while others 
are obliged to use considerable effort; the needle does not seem 
at all times equally susceptible; it often appears more easy to 
produce rotation in one direction, than in the other. There’ 
may, therefore, be a natural connection between these exper 
ments and those of M. Du Bois Raymond, who attached se 
em to dip into two cups of salt water. Dipping the fingers of 
each hand into the cups, and alternately bracing the muscles of 
actory results, but M. Humboldt was more 
to these phenomena the well-known evidences 
current, circulating around maguets, and if we 
This Journal, [2], viii, 405. 
ti hee 
