April 22, 1S98.] 



SCIENCE. 



565 



he showed that this is due to the fact that the 

 air around the tube gives forth X-rays ; if our 

 eyes were sensitive to these rays, as they are to 

 light, then such a tube would be like a light in 

 a room filled with smoke. The brightness of a 

 screen illuminated with rapidly intermittent 

 rays depends on a number of properties which 

 he enumerates. The X-rays from a platinum 

 focus plate which are most active for showing 

 images are those which leave the plate at the 

 greatest angle, but not much greater than 80° ; 

 thick plates have a relatively larger transpar- 

 ency than thin ones, that is, the specific trans- 

 parency of a body is greater the thicker the 

 body ; when two plates of different bodies are 

 equally transparent they need not necessarily 

 be so when similarly increased in thickness ; 

 the relative thickness of two equally transpar- 

 ent plates of difl^erent materials is dependent 

 on the material and its thickness, through 

 which the rays have passed before they reach 

 those plates ; the same body has different trans- 

 parencies with different tubes, ' soft tubes ' be- 

 ing those requiring a small potential and ' hard 

 tubes ' those requiring a high one ; he states 

 that all bodies are more transparent for rays 

 from hard tubes than from soft ones, and in ob- 

 taining images this must therefore be consid- 

 ered ; the quality of the rays from the same 

 tube depends on : The way in which the inter- 

 rupter works ; the Deprez form acts more 

 regularly, while the Foucault form utilizes the 

 primary current better ; on the spark length in 

 series with the tube ; on the insertion of a 

 Tesla transformer; on the vacuum; on other pro- 

 cesses in the tube which are not yet fully inves- 

 tigated. A spark gap in series acts like a Tesla 

 transformer, both giving more intense rays 

 which are less easily absorbed ; the smallest 

 pressure at which X-rays are produced is very 

 likely below 0.0002 mm. of mercury. The 

 hardening of a tube is not produced only by 

 continuing the exhaustion ; to soften a hard 

 tube, air may be admitted ; it may be warmed, 

 or the current reversed, or very strong dis- 

 charges sent through it, but the latter generally 

 changes the character of the tube ; good results 

 were produced with a tube containing a piece 

 of charcoal of linden wood. The composition 

 of the rays from a platinum anode depends 



largely on the element in the current ; the 

 quality of the rays does not change with 

 changes of the primary current, or at least 

 very little, but the intensity is proportional to 

 the strength of the primary current between 

 certain limits. He draws the following conclu- 

 sions : The radiation consists of a mixture or 

 rays of different intensity and absorbability ; thfr 

 composition depends greatly on the time ele- 

 ment in the current ; the rays produced by the^ 

 absorption of bodies are different for different 

 bodies ; as X-rays are produced by cathode rays, 

 and as both have common properties, it is 

 probable that both processes are of the same 

 nature. If two screens are illuminated with 

 two tubes of different hardness, the illumina- 

 tion being made equal, and if then replaced by 

 photographic plates, the one illuminated by the 

 harder tube will be blackened much less than 

 the other ; rays which produce equal fluores- 

 cence can be photographicallj' quite different ; 

 the usual photographic plates are very trans- 

 parent for X-rays ; in a pile of ninety-six fila- 

 ments exposed for five minutes the last one 

 showed photographic action. That the eye is 

 not entirely passive to X rays is shown by an 

 experiment ; in looking at a slit in a metal 

 screen with the closed eye covered with a black 

 cloth and by moving the head, a very weakly 

 illuminated slit will be noticed ; this maybe ex- 

 plained by assuming that fluorescence is pro- 

 duced on the retina. 



'christian science.' 



Professor J. Mark Baldwin has, in the 

 press of the Appletons, a little book called 

 ' The Story of the Mind ' (Useful Story Series). 

 He allows us to print, from the proofs, the fol- 

 lowing short passage, which may have some 

 interest to our readers in view of certain recent 

 discussions by committees of the Massachusetts- 

 and New York Legislatures : 



" All mental diseases involve disease of the 

 brain, and can be cured only as the brain is 

 cured. It does not follow, of course, that in 

 some cases treatment by mental agencies, such 

 as suggestion, the arousing of expectation, faith, 

 etc., may not be more helpful here than in trou- 

 bles which do not involve the mind, provided 

 these agencies be wisely employed ; but yet thet 



