THE CONSTANT CURRENT UNCHANGED IN ITS CHARACTERS. 45 



time the latter is continued, from the moment after contact is made up to that pre- 

 vious to disunion, except what depends upon the increased obstruction offered to 

 the passage of the electricity by a long wire as compared to a short wire. To ascer^ 

 tain this point with regard to quantity, the helix i (1053.) and the galvanometer 

 (1058.) were both made parts of the metallic circuit used to connect the plates of a 

 small electromotor, and the deflection at the galvanometer was observed ; then a soft 

 iron core was put into the helix, and as soon as the momentary effect was over, and 

 the needle had become stationary, it was again observed, and found to stand exactly 

 at tlie same division as before. Thus the quantity passing through the wire when 

 the current was continued was the same either with or without the soft iron, although 

 the peculiar effects occurring at the moment of disjunction were, very different in de- 

 gree under such variation of circumstances. 



1072. That the quality of intensity belonging to the constant current did not vary 

 with the circumstances favouring the peculiar 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 (IO71.) 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 igtiited 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. 



