certain Effects of Induced Electricity. 3 



electro-magnetism; and M. Matteucci, in his recent valuable 

 book on induced electricity, has shown some remarkable results 

 flowing from this fact. If the hammer be too near the core, 

 the former is raised before the latter has time to be fully mag- 

 netized ; and wheu a Leyden condenser is used, further time is 

 required for this to be charged. This demand of time indicates 

 the probable limit to the increase of power to which I have above 

 alluded. 



It is very curious to see the absorption, so to speak, of voltaic 

 power by the Leyden battery : when the maximum effect for a 

 given Leyden jar has been passed, the contact breaker shows by 

 its sparks the unabsorbed induced electricity which now appears in 

 the primary wire; aD additional jar acts as a safety-valve to the 

 contact breaker and utilizes the voltaic power, and so on. 



It is a question of some interest why a jar charged in the ordi- 

 nary way by temporary contact of the terminals of a secondary 

 coil will only receive a very slight charge, and give a discharge of 

 scarcely measurable length, yet when permanently connected with 

 the terminals, will give a long and powerful discharge. The follow- 

 ing is the best theory I can offer. At the moment of the induc- 

 tive action or wave of electricity, the same wire which is affected 

 by the electric impulse is unable to conduct it back again, and 

 thus to discharge the jar; while, when the jar is attempted to 

 be charged in the ordinary way, the contact, however apparently 

 of short duration, lasts longer than the single impulse of electri- 

 city, and so the coil in great part discharges the jar. Some such 

 state of the wire as that I have suggested must exist at the 

 moment of an induced current, as otherwise the wire would dis- 

 charge itself, or in other words, would never receive a charge or 

 state of opposite electricity of great tension at its extremities. 

 At one time I considered the explanation to be, that at the 

 moment of breaking contact a portion of the induced electricity 

 flies off across the discharging interval in the form of a spark, 

 and thus enables the jar to discharge itself just as the voltaic 

 arc will pass across the path of an electric spark, though it will 

 not pass tb rough a measurable distance of interposed air without 

 the spark. This theory, however, does not satisfactorily explain 

 the great increase in the charge of the Leyden phial, as compared 

 with the charge by contact. 



3rd. It must be borne in mind that each coating of the 

 Leyden phial must be connected with each terminal ; the jar is 

 not, as many have tried the experiment, to be interposed in the 

 •econdary circuit. 



The number of discharges in a given time will depend upon 

 the intensity of the battery, and its relation to the amount of 

 coated surface ; the eye cannot estimate this, but a rough mea- 



B2 



