THE FIELD OF EXPERIMENTAL RESEARCH. 125 



been produced which in 2:)art pass through cast iron nearl}' an inch 

 thick. The iron acting as a filter absorbs all rays of less penetrating- 

 power. A question may here be put, which it will be for future 

 experiment to answer: Can we, by increasing the degree of vacuum 

 in a Crookes tube by the employment of enormous potentials for 

 forcing a discharge through the higher vacuum, produce rays of 

 greater and greater penetrating power? What, in fact, may be the 

 limit — or is there any limit — to the diminution of the wave length in 

 the ether, assuming for the moment that this invisible radiation is 

 somewhat of the same nature as light, but of higher pitch, though 

 it may be unlike light in not representing regular wave trains. 



Rontgen radiation, while spoken of as invisible, is in reality easily 

 visible if of great intensity. The parts of the retina which respond 

 and so give the sensation of luminosity are apparentl}^ those around 

 the eye and not directly opposite to the iris opening. Those parts of 

 the retina sensitive to the rays are characterized by the preponderance 

 of "rods," giving the simple sensation of illumination, apparently 

 white in the case in question. The '^ cones," or those portions of the 

 retinal mem])rane whose function is believed to be the recognition of 

 color or differences of wave length, appear not to be excited b}' the 

 Rontgen radiation, or only very feebly. If this be true it would 

 account for the less intensity of the luminous effect upon those por- 

 tions of the retina near the optic axis of the eye. All this favors the 

 view that the Rontgen radiation is without sustained pitch or wave 

 trains, and resembles more a sharp noise or crash in sound. 



For pressing experimental work in the highest vacua to its limit, as 

 above suggested, we already have means at command for the produc- 

 tion of the most complete exhaustions, requiring extremely high poten- 

 tials to pass an electric discharge. We have also in well-known forms 

 of high-frequency apparatus the means for producing electromotive 

 forces limited only by our means of insulation. A recent apparatus 

 devised by me and called a dynamostatic machine gives equal capability 

 of producing high potentials of definite polarit}-, positive and negative. 

 It should not be long therefore before work is undertaken in this sug- 

 gested direction of pressing this matter of rays of high penetrating 

 power much farther than has been done. ^ The question arises whether 

 an}' such rays can exist which are not apprecialily absorbed in passing- 

 through dense substances. They would probably not affect a photo- 

 graphic plate nor a fluorescent screen. If they lost also the property 

 of ionizing a gas and causing electric convection we might not even ))e 

 able to discover them. That some influence or action in the ether does 

 actually penetrate the dense masses in space is evidenced by gravitation, 

 the mystery of mysteries. We are, however, not justified in going 

 beyond the proved facts which can only be the result of experiment:il 

 Work and close observation. All else is speculation. The energy 



