(52 
g. f. c. searlf and t. g. bedfoed 
In order to find Z, the observations for 6-^ and 6^ were repeated with other voltages 
(§ 15), with the result 
E = 8 E' = 12 E" = 16 volts. 
U= 14700 U'= 15130 U"= 15540 
From U and U', Z = (U' — U)E/(E' — E) = 860 
From U and U", Z = (U" - U)E/(E" - E) = 840 
Mean value of Z = 850 ergs per cub. centim. per cycle. 
Hence W = U — Z = 14700 — 850 = 13850 ergs per cub. centim. per cycle. 
In this case L and M are negligible, and thus, as in § 15, X/Y = QS/yOdcr. 
Taking o- as 10 ~^ ohm per centimetre cube, and putting Q = I/ 877 , since the section 
is circular, we Imve X/Y = 12 '5. But Z = X + Y = 850, and hence 
X = 787, Y = 63 ergs per culi. centim. per cycle. 
The value of Y is so small in comparison with U that it could not he determined 
satisfactorily by varying S (§ 14). A series of experiments was made in which S was 
varied, hut the small irregularities rendered the observations useless for the 
determination of so small a cpiantity as Y is in this case. [See § 41 (d).] 
§ 37. A word should perhaps he said as to the accuracy aimed at in our experiments. 
The throws were all recorded to millim., the throws themselves varying from 
25 centims. to 1 centim. The difference between ^6 and tan 2$, seldom amounting 
to more than 1 per cent., and usually much less, has generally been neglected. 
The calculations were mostly effected by a 10 -inch slide-rule, and the numbers 
recorded in the tables are the numbers read from the rule. 
Tests of the Accuracy of the Method. 
§ 38. We may now pass on from the theory of the method, and the description of 
the apparatus used for applying it in actual measurements of hysteresis, to an account 
of the tests which we liave made in order to determine if, in our experiments, the 
theoretical conditions are so nearly satisfied that the dynamometer yields accurate 
measurements of hysteresis. 
§ 39. Test hy Comparison with the Cyclic B — II Curve. —We were without the 
guidance of the completed theory till 1900, and thus till that date we did not know 
what measurements were required for the determination of the correction arising from 
the eddy currents and the finite conductivity of the secondary circuit. Under these 
conditions the only way of testing the accuracy of the dynamometer method was to 
make a cyclic B—H curve hy the use of the ballistic galvanometer, to calculate W from 
the area of the curve, and to conq)are this value witli the value of U (§ 13) found hy 
the dynamometer for the same range of magnetic force. We made this test on many 
