Wave-trains through a Conducting Dielectric. 337 



of a wave-train by its passage along the imperfectly conducting 

 wires, he assumed that there was perfect reflexion at both 

 ends of the circuit, and thence calculated the correction to be 

 applied to the experimental curve. The corrected curve ob- 

 tained in this way lay below the calculated curve. Taking 

 two points at random on his curves, I tried to calculate ex ana * 

 e + X by m y method. The results were again impossible. 



It must be remembered that in both these cases more than 

 one of the constants of the theoretical curve were simple 

 guesses, y and /3 2 //3 l in my case were both only approximately 

 known. In trying to make things square by the correction 

 of (8), we may have been attempting the impossible and 

 rightly got irrational results. I need not dwell at greater 

 length on this point : possible causes of error are numerous. 

 The non-agreement of experimental results with the equations 

 does not of course prove the wrongness of the latter, but only 

 the wrongness of their application to the case. 



I am compelled to admit that, considering the positions of 

 the maxima in my experimental curves are dependent on the 

 phase-changes and on the correction we have been discussing 

 — possibly also on other uneliminated disturbances — no great 

 weight can be attached to the accuracy of the values of the 

 dielectric constants for water, alcohol, &c, deduced on the 

 assumption that such corrections were negligible *. 



VII. The Numerical Value of some of the previous Results. 



When the expressions in sections II. and III. had been 

 obtained, the question at once arose, how far the values of b, c 9 

 fy ijr, ^r', and so on might be practically affected by possible 

 variations in the rate of damping of the incident ray. In 

 working with ordinary oscillators are changes likely to become 

 important or to remain quite negligible ? In working with 

 light are differences likely to be appreciable between flashes 

 and steady rays ? 



As regards oscillator wave-trains, the damping should 

 certainly be taken into account. The second question, how- 

 ever, must, I think, be answered in the negative, for the simple 

 reason that one cannot get a quick enough flash f. Even an 

 electric spark lasts for thousands or millions of the vibrations 

 of violet light : the rays from it would be practically steady, 

 not damped. 



The set of curves in fig. 6 is drawn for a steady ray, 



* Phil. Mag. vol. xxxvi. p. 539 ; "Wied. Ann. vol. 1. p. 748. 

 t Unless light be itself an aggregate of damped wave-trains. 



