68 
MESSES. G. F. C. SEARLE AND T. G. BEDFORD 
The agreement between 2U — U' and 3U'— 2U" is satisfactory ; it may be taken as 
evidence that the theory sketched in § 15 is practically applicable to Mr, Wills’s 
experiments. The ratio W/Y ranged from 1040 to 66,000, amd thus no appreciable 
error was introduced by neglecting the correction due to the conductivity of the 
secondary circuit. 
In the second example the specimen was a ring similar to the last, the numbers 
now being a = 1'985, 6 = '735, / = 20 centims., A = 1'46 sq. centims., hja = ’37, 
Q z= -0236, n — 50. The material was an alloy of iron and aluminium, and the 
experiments were made when the specimen was at 645'^ C. We do not know o- ; if it 
was 10“^, then X/Y varied from 430 to 1380. The results are shown in the following 
table, where it will be seen that there is again good agreement between 2U — U' and 
3U'— 2U'''. The agreement is the more significant because the eddy current loss, X, 
now forms a very considerable part of the whole energy dissipated in each cycle. 
Ho. 
Bo. 
1 
S. 
ohms. 
U. 
E = 8. 
U'. 
E'=16. 
U". 
E" = 24. 
2U - U'. 
3U' - 2U''. 
tv. 
(mean). 
X. 
E = 8. 
•20 
1747 ' 
23 
77-2 
80-3 
83-4 
74-1 
74-1 
74-1 
3-1 
•34 
3357 
23 
223-8 
251-5 
276 
196-1 
202-5 
199-3 
24-5 
•48 
4406 
23 
332-0 
390-8 
448 
273-2 
276-4 
274-8 
57-2 
•68 
5507 
73 
461 
570 
669 
352 
372 
362 
99 
1-02 
6661 
73 
615 
773 
926 
457 
467 
462 
153 
1-36 
7238 
73 
714 
917 
1107 
511 
537 
524 
190 
2-04 
8282 
73 
858 
1096 
1335 
620 
618 
619 
239 1 
2-72 
8654 
73 
952 
1214 
1472 
690 
698 
694 
258 
3-40 
8968 
73 
1007 
1264 
1528 
750 
736 
743 
264 j 
Complete Cycles and Semi-cycles. 
§ 43. The theoretical investigation of § 8 shows that the throw due to a 
complete cycle should be equal to the sum of the throws due to a pair of semi¬ 
cycles. We have not spent any considerable time in testing this point, for the 
arrangements used by us have not been well adapted for that purpose. In order 
that U shall be sensibly equal to W, it is necessary, when the specimen is a thin 
wire of soft iron, that the self-induction of the choking coil should be very large, and 
in this case, after the current has been reversed by the key, it does not at once rise 
to its full strength. Thus, if the key be worked very rapidly so as to make a pair of 
semi-cycles in quick succession, the current may never rise to its full value in the 
middle of the cycle. On the other hand, if a definite halt be made after the current 
has been reversed for the first semi-cycle, the dynamometer coil will have moved 
considerably from its zero position when it receives the impulse due to the second 
semi-cycle. It is perhaps for these reasons that we have not found good agreement 
between the throw due to a complete cycle and the sum of the throws due to a pair 
