iar results under
consideration, so as to yield an explanation of those results, was
ascertained in the following manner. The current excited by an electromotor
was passed through short wires, and its intensity tried by subjecting
different substances to its electrolyzing power (912. 966. &c.); it was
then passed through the wires of the powerful electro-magnet (1056.), and
again examined with respect to its intensity by the same means and found
unchanged. Again, the constancy of the _quantity_ passed in the above
experiment (1071.) adds further proof that the intensity could not have
varied; for had it been increased upon the introduction of the soft iron,
there is every reason to believe that the quantity passed in a given time
would also have increased.

1073. The fact is, that under many variations of the experiments, the
permanent current _loses_ in force as the effects upon breaking contact
become _exalted_. This is abundantly evident in the comparative experiments
with long and short wires (1068.); and is still more strikingly shown by
the following variation. Solder an inch or two in length of fine platina
wire (about one-hundredth of an inch in diameter) on to one end of the long
communicating wire, and also a similar length of the same platina wire on
to one end of the short communication; then, in comparing the effects of
these two communications, make and break contact between the platina
terminations and the mercury of the cup G or E (1079.). When the short wire
is used, the platina will be _ignited by the constant current_, because of
the quantity of electricity, but the spark on breaking contact will be
hardly visible; on using the longer communicating wire, which by
obstructing will diminish the current, the platina will remain cold whilst
the current passes, but give a bright spark at the moment it ceases: thus
the strange result is obtained of a diminished spark and shock from the
strong current, and increased effects from the weak one. Hence the spark
and shock at the moment of disjunction, although resulting from great
intensity and quantity, of the current _at that moment_, are no direct
indicators or measurers of the intensity or quantity of the constant
current previously passing, and by which they are ultimately produced.

* * * * *

1074. It is highly important in using the spark as an indication, by its
relative brightness, of these effects, to bear in mind certa