a ]Vace-Triice7' and Analyser, 555 



which noroes well with the Kolvin-balance readiii"; of '•4905. 

 This close agreement may be to some extent an accident, as 

 the time of 1000 periods was taken by a stop-watch, and 

 could not be accepted as being very accurate. The value 

 of I\I is not 2 parts in (iOO in error. [In the jibove calcu- 

 lation the resistance of the galvanometer, 2()0 ohms, was 

 neglected.] 



9. Fig. 2 (Plate XXII.) shows the wave-forms of the 

 current and Hux plotted from the data in the above table, 

 these are typical of such associated wave-forms when the 

 iron (of low permeability in this sample) is fairly saturated 

 at the peak ; and fig. 3 shows the curve got by plotting B 

 against H from the same experiment. The area of this 

 closed curve is proportional to the energy dissipated per 

 cycle by both hysteresis and Fuucault currents in the iron. 

 Kesearch bearing on these areas is at present in hand, and I 

 hope soon to be able to publish the results in a more complete 

 paper. 



A number of satisfactory curves for different wave-forms 

 were obtained, but cannot be reproduced here for want of 

 space. 



The Wave Analyser. 



10. The apparatus having been arranged as before, but with 

 a different commutator (see fig. 4) which effects commutation 

 2/i times per period, there will be, for each position of the 

 movable brushes, a steady galvanometer deflexion which, 



• tT 

 multiplied bv the same factor as before (Xyxr ^c>r current 



?'T "^ . . . ^^^ 



or X r- for flux), is equal to n times the instantaneous value 



of the ?/th component of the original w'ave at the alternate 

 instants of commutation (and with its sign changed at the 

 intermediate times of commutation). 



For if the same conditions as in § 2 with regard to time 

 constants be fu.filL^d the current through the galvanometer 

 will be 



_ M ^0 



and it is connnutated at times 



t, /+ J , ^ + 2;^ , &c., etc. t+[2n-l)^ , ^ + T, &c., 

 hence the quantity Q of electricity that flows through the 



