Associated cases of Current and Static Effects. 205 



to the conditions of intensity and quantity wliicli then come into 

 play; especially in the case of short or intermitting currents, 

 for then static and dynamic are continually passing into each 

 other. 



It has already been said, that the conducting power of the air 

 and water wires are alike for a constant current. This is in 

 perfect accordance with the principles and with the definite 

 character of the electric foi'ce, whether in the static, or currentj 

 or transition state. When a voltaic current of a certain intensity 

 is sent into a long water wire, connected at the further extremity 

 with the earth, part of the foi'ce is in the first instance occupied 

 in raising a lateral induction round the wii-e, ultimately equal in 

 intensity at the near end to the intensity of the battery stream, 

 and decreasing gradually to the earth end, where it becomes 

 nothing. Whilst this induction is rising, that within the wire 

 amongst its particles is beneath what it would otherwise be ; but 

 as soon as the first has attained its maximum state, then that in 

 the wire becomes proportionate to the battery intensity, and 

 therefore equals that in the aii' wire, in which the same state is 

 (because of the absence of lateral induction) almost instantly 

 attained. Then of com'se they discharge alike, and therefore 

 conduct alike. 



A striking proof of the variation of the conduction of a wire 

 by variation of its lateral static induction is given in the experi- 

 ment proposed sixteen years ago (1333.). If, using a constant 

 charged jar, the interval s, page 203, be adjusted so that the spark 

 shall freely pass there (though it would not if a little wider), 

 whilst the short connecting wires n and a are insulated in the 

 air, the experiment may be repeated twenty times without a 

 single failure ; but if after that, n and o be connected with the 

 inside and outside of an insulated Ley den jar, as described, the 

 spark will never pass across s, but all the charge will go round 

 the whole of the long wire. Why is this ? The quantity of 

 electricity is the same, the wire is the same, its resistance is the 

 the same, and that of the air remains unaltered; but because 

 the intensity is lowered, through the lateral induction momen- 

 tarily allowed, it is never enough to strike across the air at * ; 

 and it is finally altogether occupied in the wire, which in a little 

 longer time than before effects the whole discharge. M. Fizeau 

 has ap])lied the same expedient to the primary voltaic currents 

 of Ruhmkorff's beautiful inducting aj)paratus with great advan- 

 tage. He thereby reduces the intensity of these currents at the 

 moment when it would be very disadvantageous, and gives us a 

 striking instance of the advantage of viewing static and dynamic 

 phainomena as the result of the same laws. 



Mr. Clarke arranged a Bains's printing telegraph with three 



