878 UNSUSPECTED RADIATIONS. 



Their power of penetration through optujue wood or the huinan flesh 

 is diminished; and just as a phosphorescing surface which has ])een 

 struck bv ultraviolet radiations begins to glow witli a yellow or green 

 light — of a diminished wave length, as G. G. Stokes had remarked it — 

 so also the diffused secondary radiations l)ehave as if they were of 

 shorter wave lengths than the rays which originated them. The space 

 between the violet light and the Kontgen radiations is thus bridged 

 over, their analogv with light becomes closer, and the hypothesis 

 according to which they are treated as vibrations of the ether gains 

 further support. 



]\Iany other curious properties of the Rontgen rays have ])een revealed 

 duiing the last four years. The most interesting is that they are not 

 quite "invisible light." When they are of great intensity the}' become 

 visible. However, the j)ortions of our retina which aie excited ])y 

 them are th«' peripheral parts only, which contain more rods than the 

 central parts lying opposite the iris. The cones, or those constituent 

 parts of the retina which ure supposed to convey to our ]>rain the color 

 sensations, are. on the contrary, but very slightly, if at all. irritated 

 by the X-rays.' Then the more perfect is the vacuum in a Ciookes 

 tube, and conscMiuently the greater is the electrical foi'ce re<|uii"ed to 

 originate Kontgen rays, the more penetrating the}' are. In such cases 

 they pass through metals, and Rontgen himself has photographed hid- 

 lets inside a double-barreled Lefaucheux pistol, while other ex})lorers 

 have obtained radiogi'anis with lays which had passed through an 

 aluminum plate 1.4 inches thick, and excn a cast-iron plate nearh- 1 

 inch thick." The inside of a watcli which had a steel lid, the inner 

 mechanism of a lock, as also both sides of a bronze medal, were photo- 

 graphed in the same way; while, on the other hand, Goldstein obtained 

 beautiful radiograms showing the internal structui-e of a Nymphtea 

 flower, of a hei'mit cral) inside its shell, and so on.'' 



But the chief progress was made with the medical applications of 

 the Rontgen rays. The half-mystical enthusiasm of the flrst days, 

 when they were supposed to provide a new curative method, rapidly 

 subsided. But their usefulness for ascertaining lesions in the bones, 

 and for the discover}' of the actual position of strange bodies — l)ullets, 

 needles, and so on — in the human tissues, has grown in proportion as 

 surgeons have learned better to handle them. 



The pernicious effects of the invisible rays on the skin are now elimi- 

 nated l)y shortening the time of exposure which is required to obtain 



^Prof. Elihu Thomson's address delivered ))efore the American Association of 

 Science in 1899 (Science, 1899, Vol. X, p. 286; tran^lateil in Xaturwis^senschaftliclie 

 Rmidi^chau, XIV, p. 585). 



•^ Radignet, Sagnac, Hall Edwards. 



* Max Levy, "Fortschritteder Rontgentechxiik," reproduced in variou.s periodicals. 



