Law of the Induction of an Electric Current upon ttself. 19 
being no reason why there should be more of such action in one 
direction than another (i.e., on one side of cb rather than an- 
other) except on the extreme supposition of the inductive action 
being dependent on or connected with the influence of surround- 
ing bodies which there is not the slightest reason to suspect ; if, 
therefore, fb exerted any influence at all we should from the na- 
ture of the case expect to find it in the direction of cb only, and 
there is not the first fact yet known that indicates any action in 
that direction. In reference to the dynamic action of the current 
after it is established we know with all reasonable assurance that 
Jo is not felt at c. There remains then the influence of the part 
af=ab sin abc, and we may assume, also, from the analogy of 
the known law of the dynamic action, that its action is directly 
proportional to its length and inversely proportional to cb? and also 
directly proportional to the rate of development of the current in 
afborin ab. All experiments moreover indicate that the direction 
of the inductive force is at right angles to cb and in the plane abe. 
. It may be well to state before going farther that in the use 
of the term inductive force, I have no reference whatever to the 
secondary current that may result from the exertion of that force. 
henever an electric current is generated in a conductor an in- 
ductive force is exerted at any point in the neighborhood, and if 
_ the medium in which it is exerted be a conductor of electricity 
very electro-motive force without reference to the transverse 
€xtent of the elementary space in which it is exerted, but solely 
with reference to its longitudinal extent in the direction of the force, 
im the same manner as we estimate the intensity of the pressure of, 
column of water according to its perpendicular height alone. 
_%. Returning now to the fundamental law just premised let g 
-Tepresent the quantity of current flowing in ab at the end of 
the time ¢ from a given instant: - will then represent the rate 
of development of the current. Also let the distance cbh=D 
and l= the length of the electric conductor of which ab is 
an element so that ab=dJand let the angle abe=0. Then the 
 aisuctive force exerted by ab at ¢ in the direction as above 
; Stated of ed will be proportional to 
dq sin 6dl 
di. D* 
‘This formula will embrace the 2d and 3d of the above quoted 
a tons of Prof. Henry, if dg=0 for a constant current and 
ered negative when the current is diminishing in qi 
. * 
We wish to estimate the inductive force in t 
