of the /Ether in an Electromagnetic Field. 23 



and the period is 



T= 2ir 



V LO 4L 2 



LC 4L 2 



In order to compare the magnitudes of successive oscilla- 

 tions, we have 



(i.) t = 0, amplitude = A. 



(ii.) t = T, amplitude = Ae V ~- ^ 



4L 



As R is increased, since R 2 <-tvj both factors in the index of 



\j 



e in (ii.) increase, and therefore the amplitude diminishes. 



By introducing a resistance, therefore, into the circuit the 

 effects of second and succeeding oscillations may be rendered 

 negligible. In the secondary circuit of our condensers we 

 accordingly introduced a resistance which experiment showed 

 to be sufficient to fulfil this object. 



The object of the spark near c is to produce electric waves 

 in the direction cb, those in the direction cd being screened 

 off by a copper plate. If, then, these electric waves are 

 accompanied by an actual motion of the sether in the direction 

 of propagation, it should be at once apparent by the displace- 

 ment of the interference-bands. In actual experiment this 

 spark-gap was at first short-circuited ; then one of us observed 

 the bands produced by the spark at the collimator, and 

 watched if he could detect any displacement when the short 

 circuit was suddenly removed. In repeated experiments, 

 however, no motion whatever was discernible, although a 

 displacement for one fifth of the breadth of a band — a displace- 

 ment which would be produced by an alteration of the differ- 

 ence of phase by one tenth of a period — would have been 

 visible to the eye. 



In our next experiment the spark-gap at c was removed, 

 and the wires of the secondary circuit were led to earth after 

 passing round the three sides ab, be, cd of the square — parallel 

 to the beams and so as to include the beams between them. 

 The same damping was kept in this circuit. The wires were 

 insulated on paraffin blocks and strips of tinfoil hung over 

 them to a depth of 3 centim. throughout their length, thus 

 giving sides to the electric waves (fig. 2). 



When the secondary plates discharge, a positive current 

 runs down the one wire and a negative current down the 



