A new method for measuring the momentary values 

 of the aiternating ciirrent. 



by Ph. Dr. Vlad. Novàk, professor of the BohemiaQ Technical Highschool at 



Brunn, 



and Ph. Dr. B. Macků, assistant of the Physical Lahoratory of the Bohemian 

 Technical Highschool at Brunn. 



The indirect methods for observing the momentary values of the 

 aiternating current hâve their common origin in Jouberts' (C. R. 91. 

 161. 1880.) idea of the momentary contact. This arrangement however 

 suffers hrom the instability and indefiniteness of the contact, which — as 

 Fbanke (Elektrot. ZS. 20. 802. 1899 and ZS. f. Instrkunde 21. 11. 

 1901) did — must be specially provided for good measurements. 



We changed the mechanical contact of Joubert in an optical 

 method, which allows to measure the momentary intensity of the ai- 

 ternating current by means of a Polarimeter, which is illurainated 

 periodicaily in the moment determining the phase of the measured 

 intensity. The method was tried in ťwo arrangements, which are sche- 

 iiiatically illustiated in figures 1. and 2. The axis of the used 

 dynamo is provided with a circular dise B with a radial linear ap- 

 perture. The light from an electric arc-lamp L comes through this 

 apperture only for the very moment, in which the slit coïncides with 

 the apperture of the dise A, which fixes the phase of the measured 

 intensity. The periodical illumination of the Polarimeter by means of 

 a systém of mirrors in both cases, was accomplished in the first case 

 only with two mirrors, the lamp beeing mooved horizontály as also 

 verticaly according the moved hole in the dise A. In the second case 

 five mirrors were used, systém of four being arranged in that way, 

 that the lamp stood flxed in the axis of the dynamo. Both methods 



