1883.] on Meters for Power and Electricity. 239 



on its opposite side. In this instrument, the inclination of the wheels 

 is efiected by an arrangement of coils of wire, the main current passing 

 through two fixed concentric solenoids, and a shunt current through 

 X great length of fine wire on a movable solenoid, hanging in the 



1 space between the others. The movable portion has an equal 

 :iumber of turns in opposite directions, and is therefore unaffected by 



[Qiagnets held near it. The effect of this arrangement is that the 

 3nergy of the current, that is, the quantity multiplied by the force 



I iriving it, or the electrical equivalent of mechanical power, is 



I aieasured by the slope of the wheels, and the amount of work done 



' by the current during any time, by the number of turns of the cylinder, 

 ivhich is registered on a dial. Professors Ayrton and Perry have 

 ievised an instrument which is intended to show the same thing, 

 rhey make use of a clock, and cause it to go too fast or too slow by 

 :he action of the main on the shunt current, the amount of wrono"- 

 less of the clock, and not the time shown, is said to measure the work 

 lone by the current. This method of measuring the electricity by 

 he work it has done, is one which has been proposed to enable the 

 dectrical companies to make out their bills. 



The other metl\od is to measure the amount of electricity that has 

 )assed without regard to the work done. There are three lines on 

 vhich inventors have worked for this purpose. The first, which has 



, )een used in every laboratory ever since electricity has been under- 

 tood, is the chemical method. When electricity passes through a 

 alt solution, it carries metal with it, and deposits it on the plate by 

 v'hich the electricity leaves the liquid. The amount of metal deposited 

 5 a measure of the quantity of electricity. Mr. Sprague and Mr. 

 Cdison have adopted this method ; but as it is impossible to allow 

 be whole of a strong current to pass through a liquid, the current is 

 ivided, a small proportion only is allowed to pass through. Pro- 

 ided that the proportion does not vary, and that the metal never has 

 ay motions on its own account, the increase in the weight of one of 

 le metal plates measures the quantity of electricity. 



The next method depends on the use of some sort of integrating^ 

 lachine, and this being the most obvious method, has been attempted 

 y a large number of inventors. Any machine of this kind is sure to 

 o, and is sure to indicate something, which will be more nearly a 

 leasui-e of the electricity, as the skill of the inventor is greater. 



Meters for electricity of the third class are dynamical in their 

 3tiou, and I believe that what I have called the vibrating meter was 



i le first of its class. It is well known that a current passing round 

 ■on makes it magnetic. The force which such a magnet exerts is 



Teater when the current is greater, but it is not simply proportional; 

 ' the current is twice or three times as strong, the force is four times 

 ■ nine times as great, or generally, the force is proportional to the 

 [uare of the current. Again, when a body vibrates under the influ- 



j ice of a controlling force, as a pendulum under the influence of 

 •avity, four times as much force is necessary to make it vibrate twice 

 Vol. X. (No. 76.) . b 



