lyy M. Ampere in his Electro-Magnetic researches • 415 
and the conductor, is always a right one, when the directive ac^ 
tion is the only one which takes place. 
The apparatus by which M. Ampere established the exis- 
tence of an attractive and repulsive action, between an electric 
current and loadstone/ without allowing the directive action to 
combine with them, is shewn in Fig. 9., where ABC is a stand, 
whose arms BEG, BFH, support the horizontal conducting 
wire KL, near which is suspended a small cylindrical magnetic 
needle MN, from the point C, by means of a silk fibre, and 
sometimes by its south, and sometimes by its north pole. With 
this instrument M. Ampere proves, that when a needle has its 
axis perpendicular to a conductor, joining the two extremities 
of the pile, the conductor will attract the loadstone, when its 
south pole is to the left of the. current which acts upon it, that 
is, when the position is that which the conductor and the load- 
stone tend to take in virtue of their mutual action, and will re- 
pel one another when the south pole of the loadstone is to the 
right of the current, that is when they are kept in a position op- 
posite to that which they tend to give one another mutually. 
In order to prove still more clearly the identity between the 
currents in voltaic conductors and those in magnets, M. Am- 
pere procured two small and strongly magnetised needles, fur- 
nished in the middle with a double brass hook, carrying an ar- 
row, which points out the direction of the current of the magnet. 
One of these needles is shewn at the right hand side of Fig. 1. 
where a 5 is the needle, cd the double hook, and the arrow. 
By means of c d, the needles adapt themselves to the conductors 
AB, CD, Fig. 1. in a situation where the line which joins their 
poles is vertical, and where their currents, always parallel to the 
conductors, can be directed either in the same or in opposite di- 
rections. Having produced attractions and repulsions between 
the conductors AB, CD, by making the electric current pass 
along both, it is then made to pass only along one, and one of 
the needles is placed on the other, so that the current in the 
needles is at first in the same direction as it had before been in 
the conductor to which it is adapted. In this case, we observe 
the phenomena of attraction and repulsion, which were exhibited 
by the two conductors. The same needle is then placed so as 
to have its current in an opposite direction, and the inverse phe- 
