1885.] NEW YORK ACADEMY OF SCIENCES. 91 



between tlie electro-motive force lost in the circuit, and the inten- 

 sity of the current. 



This is a constant for any solid so long as its form and temper- 

 ature are not changed. 



The volt, and ampere are more difficult to define, and perhaps 

 I can best make their meaning clear by making use of analogous 

 hydraulic formuhy. 



Understand me, this is only a case of analogy. I do not say 

 that electricity is a fluid, nor would I like to say that there is a 

 current of electricity, or that it flows one way or the other. 



The volt may be said to represent the pressure or head of the 

 assumed current of electricity, and the ampere to represent the 

 intensity or weight of the current passing in one second. Lord 

 Kayleigh has carefully determined the weight of silver precipitated 

 from a solution of nitrate of silver by one ampere. It is 0.06708 

 grammes per minute, or 4.0248 grammes per hour. 



Referring to Fig. 1, if W equals the weight of water that 

 passes the poiut A in a pi])e, in one second, and li the loss of 

 head, we have for the Avork done in one second, W h foot lbs. 



Again, if I represents the intensity of a current passing the 

 point A in a second, and E the difference of potential in volts 

 between B and A, we have for the work done in one second I E 

 volt, amperes, or Watts. If we divide W h by 550 ft. lbs. we 

 obtain the horse-power. 



"^^In the case of the pipe, if it were level, the loss of work would 

 be due to friction, and transformed into heat. 



m 1 V" T -nr I W v' M v' 



Thus h = ^ and W h= = 



2g 2g 2 



Joule has shown us by experiment that the heating of a wire 



■pa 



conductor is proportional to P E=IE=— -, or using the anala- 



h i! 



gous hydraulic formula, the heating is, W Xtu = W h=^ 



W 



I E 

 Again, — ;-= work per second in kilogi-ammetres, but an 

 9.81 



