somewhat analogous to Newton s Rings. 



81 



single pair of tinfoil sheets, next with the bridge at BB', then again 

 without the bridge but with an abnormal part of two pairs of sheets, 

 and so forth, the readings with and without bridge being always 

 alternated. 



The result is plotted in the curve shown in fig. 6, the lengths of 



FiQ. 6. Analogy to Newton's Rings by Reflexion. 



i-O 



5 ' 9 

 S '8 



im-. t 3 4 5 6m. 

 Lengths of the abnormal part 

 of the Secondary. 



the abnormal part being taken as abscisses, and the ratios of electro- 

 meter throws as ordinates. 



On this curve two apparently anomalous humps may be noticed in 

 the neighbourhood of 1*5 m. and 5*5 m. lengths of the abnormal 

 part. These, however, are not due to errors of observation ; for, on 

 carefully repeating the experiment in these regions the first results 

 were confirmed, as shown by the double dots made at those places. 



A few readings were also taken with the above general arrange- 

 ment, but an abnormal part, consisting of the ordinary wires nearer 

 together, just as in Experiment VI. It was thus found that the 

 electrometer throws were about three times as great with an ab- 

 normal part a quarter- wave long as with one a half-wave long. 



Experiment VIII. An Abnormal Part which Produces no Reflexion. 



Having thns far experimented with the desired interference 

 phenomena, and discussed the various disturbances involved, it now 

 seems of inferest to notice particular forms of the abnormal part 

 which reflect no portion of the wave-energy incident upon them. 

 This and the following experiment were tried as tests of the truth of 

 the theory for a single reflexion. 



However, to establish the entire absence of reflexion would be very 

 difficult with the single-needle electrometer previously used, because 

 the slightest irregularity of the primary sparking might be mistaken 

 for the effect of reflexion. And no repetition of observations, however 

 extended, would justify the conclusion that the energies transmitted 



VOL. LVII. G 



