274 



Mr. F. T. Trouton on the Acceleration 



Practically the quickest method for determining the positions 

 of maxima and minima for B is to plot the curve represented 

 by this equation in each particular case. The curve shown in 

 fig. 5, PL VI. is that where k=30c, Z = 22c, and \=72c. The 

 abscissa represents the distance, measured in centimetres, from 

 the reflector to the point, while the ordinate multiplied by A 2 

 represents the intensity or square of the amplitude of the 

 magnetic force of the stationary wave at the point. The 

 dotted line indicates the intensity of the direct radiation, to 

 which the curve is seen to approximate as r increases in value. 

 The curve is seen to be going off the limits of the paper on 

 the side next the reflector ; but it must be remembered that 

 in this region the formulae used have but an indirect inter- 

 pretation as the finite size of the reflector becomes important, 

 and that there is involved the idea of the aether here being in 

 special commotion, so that reflexion may in a certain sense be 

 looked upon as taking place before really reaching the mirror. 



On examining the curve the first minimum will be seen to 

 occur at about 24 c from the reflector, which agrees suffi- 

 ciently well for an approximate method of calculation with 

 the result of experiment, which for a wave-length of 72 c 

 gives the first minimum at about 25 c* And in fact we 

 might expect, on looking at the curve, that the experiment as 

 made would always tend to give the minimum a little beyond 

 its true position ; for if the spark-gap be set to just observe a 

 spark of, say, the direct waves' intensity, and if the distance 

 be bisected between the positions to right and left of the 

 minimum where sparking is observed to commence on moving 

 along the " receiver," this point will be too far out, owing to 

 the portion of the curve to the left being steeper than that to 

 the right. This is well marked when working with the spark- 

 gap comparatively open ; that is to say, various positions are 

 then obtained for the minimum according to the width of the 

 spark-gap. This was experimentally noticed before the curve 

 was plotted. 



The curve indicates at once the reason why it is difficult to 



* In this Table the results of experiments with different wave-lengths 

 are shown in the third column. 



X. 



fX. 



Min. 



72 

 68 

 60 

 56 



27 

 25-5 

 22-5 

 21 



25 

 24 

 21 

 19 



