400 RECENT PROGRESS IN PHYSICS. 



unit of resistance, the unit of current produces 0.0000176 units of heat 

 per minute ; but the resistance to conduction of such a platinum wire 

 as can easily be calculated, is equal to 6 and consequently by the unit 

 of current, 0.0000176 X 6 =r 0.0001 units of heat would have been 

 produced in it. The increase of temperature in the platinum wire 



from the discharge of the jar for -^- = 1, viz: 0.000000768 is there- 



o 



fore nearly yj,^ of that produced by the unit of force of the current 

 durino; one minute in the same wire. When 5=1, i. e. when the 

 electricity is accumulated in one of the jars (mentioned in the experi- 

 ment above quoted,) q must also be equal to 1 . For s = 1 and q = 10, 

 i. e. when the jar is charged with 10 sparks from the measuring jar 

 under the circumstances formerly explained, then its discharge must 

 produce in a metallic wire an increase of heat nearly equal to that 

 produced by the unit of current during one minute in the same wire. 

 But to charge the jar with q = 10, the machine will scarcely require 

 to be turned for one minute, and therefore the inference might be 

 drawn from a superficial investigation of the production of heat, that . 

 turning the machine for one minute would produce a quantity of elec- 

 tricity equal to the chemical unit of the galvanic current. 



But that such a comparison, or rather such a conclusion from the 

 comparison can not at all be admitted, is evident from the fact, that 

 by means of the electrical machine no perceptible decomposition of 

 water can be obtained, while one cubic centimetre of detonating gas 

 ought to be readily evolved per minute. 



But a more careful investigation soon shows that the discharge of 

 the jar and the galvanic current act under entirely different and not i 

 comparable conditions, in producing heat in the Avire. 



The same charge of the jar when passing more slowly through a 

 wire produces less heat in it, and the increase of temperature becomes 

 imperceptible as soon as the time of discharge reaches a measurable 

 duration ; if, therefore, the quantity of electricity, obtained by turning 

 the machine for one minute, when accumulated in the jar produces by 

 its discharge perceptible heat, the same quantity of electricity dis- 

 charged through the wire in a continuous current during one minute, , 

 will not perceptibly raise the temperature of the wire. But only such i 

 a current can be compared with the galvanic. In order to compare e 

 the electricity of the machine with that of the battery in relation to ) 

 quantity, we should be able to measure the quantity of heat which is - 

 produced in a metallic wire by the electricity passing through it from 

 the conductor of the machine. The instantaneous discharge of an 

 accumulated quantity of electricity cannot directly be compared with 

 a continuous current. That the process by which heat is evolved in 

 the discharge of the Leyden jar is entirely different from that of the .'' 

 galvanic current, is also evident from the fact, that with the former i 

 not only the quantity of electricity discharged through them is con- 

 cerned, but also the area of surface upon which it was previously 

 distributed ; thus, in the production of heat by the discharge of the 

 jar, factors come into question which with the current do not appear 

 at all. The galvanic current and the discharge of the jar have, as far 

 as regards the production of heat in metallic wires only this in com- 



