NOMOS. 25 



copper wire half a mile in length and divided in 

 the middle, and the time is noted when the spark 

 appears at the ends of the wire and at the division. 

 In this experiment the wire is bent in such a way 

 that all the sparks are placed in the same field of 

 vision. And what is the result ? The result is, that 

 the spark at the middle is sensibly behind the sparks 

 at the ends of the wire (which are simultaneous) ; 

 and, being behind, it is evident that the electricity 

 has not been conducted from the ends to the middle 

 of the wire without a sensible loss of time. The 

 conduction has not been instantaneous. 



" If now," as Dr. Faraday reasons, e { we leave the 

 arrangement at the middle and two ends of the 

 long copper wire unaltered, and, removing the two 

 intervening portions, replace them by wires of iron or 

 platina, there will be a much longer interval between 

 the appearance of the middle spark and the terminal 

 sparks. If, removing the iron, we were to substitute 

 for it only 5 or 6 feet of water of the same diameter 

 as the metal, we should have still greater retard- 

 ation. If from water we passed to spermaceti, 

 either directly or by gradual steps through other 

 bodies (even though we might vastly enlarge the 

 bulk, for the purpose of avoiding the occurrence of a 

 spark elsewhere than at the three proper intervals), 

 we should have still greater retardation, until at 

 last we might arrive, by degrees so small as to be 

 inseparable from each other, at actual and permanent 

 insulation. What, then, is to separate the principle 

 of these two extremes, perfect insulation and perfect 

 conduction, from each other, since the moment we 



