﻿1024 Prof. V. Karapetoff on General Equations 



The critical isotherm calculated from the values of the 

 constants obtained above is shown in fig. 1 as a continuous 

 curve. How nearly it fits the measurements for isopentane 

 down to about \ the critical volume is seen by examining 

 the circles which represent experimental points. 



The following values given by experiment and also by 

 various equations for the case of = J are useful for 

 comparison to show the success and defect of the revised 

 equation. 



Experiment. Van der Waals. Dieterici. Porter. 



« = 2'15 4 j Infinity 1-56 



etj3 = l'07 2 j Infinity '782 



XCIII. General Equations of a Balanced A Iternating- Current 

 Bridge. By Vladimir Karapetoff, Professor of Electrical 

 Engineering, Cornell University, Ithaca, iV 7 .! 7 ".* 



IN the last few years the use of the Wheatstone bridge 

 for the measurement and comparison of inductances 

 and capacities has considerably increased, partly due to 

 developments in the art of electrical communication, and 

 partly because of improvements in the sources of high- 

 frequency sinusoidal currents. Old classical arrangements 

 of alternating-current bridges have been further developed 

 and new arrangements evolved f. This seems, therefore, to 

 be an opportune time to deduce a general equation of the 

 a.c. bridge which would comprise the various actual bridge 

 arrangements as specific cases. Such a general formula 

 gives a bird's-eye view of the existing bridge connexions 

 and will enable new bridge arrangements to be devised 

 without deducing fundamental equations in each case or 

 constructing vector diagrams. It is hoped that the general 

 formula (D) given below will serve these two purposes. 



Some time ago Dr. Poole showed} that the currents 

 and voltages in the usual arrangements of an a.c. bridge, 

 when balanced, can be represented by comparatively simple 

 vector diagrams from which the relationship between the 



* Communicated by the Author. 



t See D. I. Cone, " Bridge Methods for Alternating-Current Measure- 

 ments," Trans. Amer. Inst. El. Engrs. vol. xxxix. p. 1743 (1920). 



% H. H. Poole, " On the Use of Vector Methods in the Derivation of 

 the Formulae used in Inductance and Capacity Measurements," Phil. 

 Mag. vol. xl. p. 793 (1920). 



