somewhat analogous to Newtoiis Rings. 



EXPERIMENTS. 



73 



The chief experiments made will now be dealt with in the following 

 order : 



(1.) Undesired interferences of separate wave-trains. Experi- 

 ments I III. 



(2.) Estimate of rate of decay of waves. Experiment IV. 



(3.) Analogy to Newton's rings by transmission under improved 

 conditions. Experiments V and VI. 



(4) Analogy to Newton's rings by reflexion. Experiment VII. 



(5) Abnormal parts which produce no reflexion. Experiments 

 VIII and IX. 



Experiment I. Undesired Interferences of Distinct Wave-Trains simul- 

 taneously reflected at and transmitted through the Abnormal Part of 

 the Secondary. 



To investigate this question the arrangement of apparatus shown 

 in fig. 1 was adopted. The abnormal part consisted of a single pair of 

 tinfoil sheets each 50 cm. long and 32 cm. deep, the two being hung 

 immediately opposite each other, one on each wire of the secondary. 

 The total length, SAD, of the secondary was 162 m., the distance 

 SAM was varied from 75 m. to 90*5 m. by steps of 0'5 m. each. 

 Electrometer readings with and without the sheets were taken alter- 

 nately in order to eliminate the possible errors due to irregular work- 

 ing of the primary sparks. The observations taken are shown in 

 Table I. 



The result is graphically exhibited in the curve, fig. 2. 



Fio. 2. Curve showing Undesired Interferences. 



Distances of middle of tinfoil sheets from beginning of Secondary. 



Experiment II. Interferences as in Experiment J, but with Thin Iron 

 Wires at the end of the Secondary. 



Various experiments were made with the secondary lengthened 

 about 70 mm. by the addition of thin iron wires, in the hope that they 

 would absorb all the incident waves and thus do away with their 

 repeated coursings and consequent interferences. The result was an 



