506 L. P. Wheeler — Dispersion of Metals. 



At present, however, and certainly as far as the experiments 

 under discussion go, there seems to be no light on this ques- 

 tion. If the fact of decreasing electronic absorption with 

 increasing frequency be granted, nevertheless, then the above 

 hypothesis appears to be sufficient to reconcile the experi- 

 mental data.* 



It remains to discuss equation (9) in the light of the experi- 

 ments. Since the values of r can now be regarded as known 

 (from equation (8)), it is obvious that this equation gives us the 

 means of ascertaining the values of K throughout the spec- 

 trum. Further it will be seen that the value of K consists of 

 two parts ; that due to the term involving r, and that due to 

 n*(fc 2 — 1). The latter is the value of K to be expected if no 

 free electrons were present ; hence we may speak of the " dielec- 

 tric" and the " conductor" parts of K. In order to trace 

 separately the influence of these two parts, the values of each 

 are given in the tables : in column 7 the values of n\fc 2 — 1) as 

 computed from columns 3 and 4, and in column 8 (headed A) 

 the values of the conductor term as calculated from the right 

 hand side of equation (9). In column 9 is given the algebraic 

 sum of the two terms, or K, which latter is also shown in the 

 broken line curves in the upper halves of the figures. 



It is obvious from these results, in the first place, that the 

 values of K are not zero — the value demanded by a perfect 

 conductor. In the second place, we observe that the presence 

 of free electrons (the conductor term) plays the preponderating 

 role in the so-called dielectric constant, particularly at the 

 shorter wave lengths. The dielectric term, however, increases 

 relatively to the conductor term with increasing wave length 

 in all of the metals except cobalt. Thus in silver the dielec- 

 tric term increases tolerably uniformly throughout the region 

 covered by the measurements from about 1 per cent to about 

 80 per cent of the conductor term : in copper from about 0*1 

 per cent to 33 per cent ; in gold from 1 per cent to 27 per 

 cent ; in nickel from 1 3 per cent to 29 per cent ; while in cobalt 

 the proportion varies from 5 per cent through a maximum of 



*It may be possible that the increase in r is to be attributed to a transition 

 layer or region of interpenetration of air and metal. This might naturally 

 be supposed to be relatively poorer in free electrons than the main body of 

 the metal. Then, if at the longer wave lengths the radiation did not pene- 

 trate this layer, while at the shorter it did, the increase in r would be ex- 

 plicable. This hypothesis, however, even more than the former, fails to 

 elucidate the mechanism of absorption. If it is adopted it would seem to be 

 necessary to attribute the major part of the absorption to the relatively fixed 

 ions. Hence further assumptions as to the nature and connections of these 

 ions would be necessary, in order to explain the existence of the type of 

 absorption which experiment reveals. However, this is hardly the place in 

 which to follow further such speculations ; the experimental basis is not 

 sufficient either in extent or precision. 



