Recent Work With Rontgen Rays

Thursday, April 30, 1896
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6x4 NATURE [APl{IL 30, 1896 sensitive surface of lbe plnutogrnpltic film. I brtve obtained ronsidembly better results uith n finely ground sample of lungstztte of enlciunt, prepared Gvr me by Messrs. llopktn nnd \\'i|linn\s. This nmy he med either in loose pmult-r or tnrule up uillt gum inln rt pnsle nnd dried. “\\'itb this subslarnee it is easy tn obtnin sharp and fully- ex|\<»st-tl nvwttir-.~= ofthe multi in f..~..» nw t.. mr ~.-\-m\.|= “im n tnnderztlcly exritrrl Iulw, uilb ubirli, u-i\|\ rmlinnry nrmngc- tncnls, unc tn t\\'<\ minutes' e\p¢\sure uunld be ttecussnry. “I lmve also tried sonic spceinl plates pu-|w\red for me by Ncssrs, Marion, into the sensitive emulsion of wliirli fluorescent substances such ns pmttlcrvd llunr-spur :intl <':\|ciutn tungstrtle were sntmlrrccti heroic a|»,»1a.~mi.,.. to tlte Him, '|~|\.»“,;i\ the results so hir r»l»t:\inet| by this ntetlnnl are not very sntislnclnry uvving to gr:\nnl:trily. tlte prescttrc of tbv llurvrescettt stibslnnee i|\ the plnxlogrnplrir Elin nppmus tntulnubledly tn i|\r|t~|\\e ilu sensitireness tu t te r:\)'s. “ There is :\ wide Held Dir further research un tlte lilies :tbove indicated, bulb with regard to suitable tluorescent substances and the best method Iiur their npplirnliniif' /\ paper by Ur. Ferflinztntlo I iinni, uftbe Regiu lstilutoTcc|\icn, I‘erugi:\, is nf itnporlnnve in this ctninerlion, nnd the following trattslntiun ofit, by Mr. (E. ll. Baillie, will be uceful ln chemists who :ire preparing Iluureseent =n|t< hr use with Riinlgen mys z “ Some dztys ago Prof, Rnnm nnllcrl my attention to the lele- grmn sent by Edison to Lord Kelvin, nnd pul»Iiosures. Nou' it ntny No. 1383.vo1.. 53] occasionally happen thnt a permanent record is desirable 0. what must be dune nlnuost instantxtneously. That point I think ouglu to be renrlxetl ere lung. “Some weeks ngo I recunlerl it photo of the elbow-joint in ti niimues, nnd that nt n lime when ne did not understand the tubes ns well as now. Since then I l\n\'e |>bt:\ined rccortls of tnetnllic objects in hnlf it sceuntl, and tlte bones of thc hnnd in six seconds, uitbuut the nirl of fluorescent screens. \\`h:\t we desire most, l\o\\~e\'er, in practice is a better Cronkes’ tube for fluorescent srrcvns in direct vision. ¢\\ present I go while thetnbe is being e\hnustcd, :tnd lest tbc result before it is taken off lbe pump. \\'||en I mn examining nn nlject with the screen, or about to pliotogmplt, I bent the tube nnd keep thc current passing through \|nli| the lnaxiniuln ufleet is oblztinetl. I l\:\\'c now seen by this ntenns the dill't-rent lvnws ul' the t“r:|. Foreign bodies in tlte extremities are, as it rule, cnsily seen. " For the evtminxttion of the cavities inside tlte head, e._qz the nltlruin, nr nioullr, or pltnrynw, also the teeth, I now place fluor- escent screens in the xnotttli, nnd the Crookes‘ lube outside, either rtbove or below the level of ll\e buccal cavity as required, and shnrp inmges me lluis obtnined on thc screen of not only foreign hotties, but also of the bones of the fnce, nnd roots of the teeth ns well. “Other tissues llmn the bones are now yielding. I have plmtogmphetl the side of the neck, and shown the tongue, lyoid bone, the plmry val cavity, cnrlilages of larynx and tmchin of the living ndulb snb`cct. “ 1 l presenl we cannot nllord to ignore :my aid, and hence ne nre glnrl to hnve such hints as the fluorescent screens in phnlogm|\l\)7; but it is not unlikely lbnt all such will be more or less dispensed with ns n better source of the X-rays is oblnined, \-ir. it still better Croolces‘ tube." Since the above wns written, nnd in cnnsiilemtion of the <|nexllon nt issue, In. Mncinlyre informs us that he has made a further series of experiments on the question of rapid exposures. The tube used was one nf the now well-knonn ordinary focus tubes, mnde in tilnsgnw. lle bits obtained a well-defined inmge of metallic objects, nnd distinct, though faint, image of the bones of the fingers with one Hash of the Crookes’ tube. produced by n single vibration of the mercury interrnpter, a large coil giving an eleven-inch spark, antl, of course, without using nny fluorescent screen. Wlmt the extent of the time of ex- posure wits cnunut be said, b\|t he describes it as un unknown, unnueasuretl, snmll frnction nf at second. ln another experiment he wns able In obtain n distinct image ol' the bones of the fore~ arm with sixty similnr flashes of the tube. l‘ro(. 0. N. ltnod found indications of reflection of Rilntgen rays from tt platinum surface nn March 9, nndon March I3, rtfler nn exposure often hours, be obtained :t good negative, cnpnble of furnishing prints, ofa piece of iron wire netting rellected from n sheet of ordinary platinum foil and through at plnle of nlunrintim (Srmrrr, Mnrch 17). The conclusion he nrrived nl from inspection uf tlte inmge was that “in the act of rellectimt from n metallic surface the Riintgen my; behave like ordinary light." I-Ixperinwnts nmde to nscertnin the per- centage of ll\e mys relleclerl, intlicntcd that plntinum foil reflected the t/260th ptul ofthe X-rays incident nn it at an angle of 45°. Upon the question of reflection and refraction of Rtinlgen mdinnce, l’ruf. l’upin pointed o\\t in his paper read before the New York 1\c:ttlcmy of Science, on April 6. that it was dis- cussed by I’rof. Riintgen in Sections 7 and 8 of his origina essay. Neither by photography nor by the fluorescent screen could Prof. Riintgen detect an appreciable refraction with cer- tainly. A reflection fmtn melnllic surfaces in the immediate vicinity of :t photogmpltic Elnt uas detected, “ but," translating l{iintgen's own words, “if \\'e connect these fncts with the observation that powders are quite as tmns _ rent as solid bodies, and that, moreover, bodies with rough sur aces are, in regard to the tmnsmission of X-mys, as n-ell as in the experiment 'ust de- scribed, the sruue ns polished bodies, one comes to l e con- clusion thnt re ulnr reflection, ns nlrertdy stated, does nnt exist, but that the lzmtlies bchnve to the X-rays ns muddy media do to light." " In (nee ofthesenlrserr-:uion<,” continues l‘rot'. Pupin, “ l’m|2 Rom|'s nnd M r. Tesln's experiments must be interpreted ns :\ conlivtttnliun of l’r0f. l{&in\gcn`s results, nnd not as it

APRIL 30, 1896] NA TURE 615 demonstration ol' the existence of a regular reflection. Mr. Tesla infers regular retiection front his theory of bombardment. His experimental method is the saute as that of Prof, Rond; that is, he places a reflecting plate at an angle of forty»iive degrees to the direct ray, and then places the photographic plate at right angles to the direction in which the reflected ray should pass if regular retiection existed. On account ot' the greater power of his apparatus, his time ol' exposure was one hour, whereas that of Prol2 Road was ten hours. lt is evident, how- ever, that an etleet upon the photographic plate does not prove the existence of regular reflection,” In his own experiments on reflection, Prof. Pupin aimed at getting rid ofthe photographic plate and substituting the fluor- escent screen in its lace. He concludes as tlollows :-“ These ex rimentstprove beyond all reasonable doubt that the Riintgen ranliince is ifliusely scat- ~tered through bodies, gases not excepted. We may cull it' dilTuse retlection, if we choose, rovirled that \ve do not imply, thereby, that we must necessarily assume an internnl inter-molecular regular reflection, in order to explain the phenomenon. For if a pull' of smoke he forced through a pile of wood, some of it will come out pretty well scattered, a though we cannot speak here of a reliection in the ordinary sense, but rather of deflec- tion, reserving the term ‘ reflection ’ for those particular cases in which the angle of incidence is equal to the angle of detlection. It might turn out, for instance, that the X-rays are due to a circulating motion of ether, and that the stream lines are detlected and diffusely scattered within the molecular interstices of pondemble substances. Appearances seem to speak more in favour of this view than in favour ol' 3 wave motion ot ether. The diliuse scattering of the Riintgen radiance by bodies placed in its path. may be also described by saying that :wry .rzlbslame 11//re/zusrl/ykl'/:ri M I/te aftion qf .f/ze .\'»ra}/r decal/us nz radiator q' lim: rays. _ . . The fact that opaque bodies, like metals, are less effective in produc~ ing this secondary radiation, leads to the conclusion that there is in these bodies an internal dissipation ofthe Riintgen radiance much greater than in the case ol transparent dielectric sub- stances. A properly constructed bulometer should give us much information on this point, and it is my intention to nike up this subject as soon as time and facilities will permit. These diIi`u» sion etiects, which are present even in air, bring the Rdntgen radiance into still closer resemblance to the principal features of the kathode rays which were studied by Proh Lenard, The -difference in their behaviour towards magnetic force is still to be explained. Is it not pnsible that this magnetic effect in air is masked by the diffuse scattering of the X-rays P ” Our American correspondent says :-“Tesla has found that the X-rays are retlected from certain metals tested in the same order as in VoItu‘s electric contact series in air. Zinc reflects 3 per cent. at an angle of 45". Below it stand lead and tin, but his observations do not yet show which reflects more highly. Below these in order come copper and iron about the same, then silver. His first observations led him to infer that magnesium would reflect still more than zinc, and sodium most of all. Subse- quent experiment has verified the conjecture as to magnesium; but sodium has not yet been tested. By availing himself of the reflection front a zinc cone, he has taken a picture of the ribs of an assistant at a distance of four feet from the vacuum tube, and with an exposure of forty minutes. His ap- paratus is so constructed that the bulb or bulbs are at the large end ofthe cone, and the subject at the small end, where the rays are concentrated. The cone or funnel is constructed at an angle less than 3o°, so that the incident ra s are reflected ntore than 3 per cent; and especially more tlie small end of the funnel the rays approach within a very few degrees of parallelism with the reflecting zinc. Proi Tesla thinks the theory that the X~rays consist of streams of radiant matter, is confirmed by these results. He has not yet been able to detect any refraction of the X-rays.” In the summary ot' work done in connection with Riintgen rays (page 522), we give an account of experiments made by Prof. joly, which demonstrate the existence of reflection. “ In confirmation of these experiments,” writes I\lr. Alfred W. Porter, “mayl point out that a similar phenomenon to that described by Proli _Ioly has been present on all my skeletal radiographs. Immediately surrounding the sharp geometric shadow oi the llesh of the fingers a black line exists on the nagaliw. This is especially noticeable where two fingers overlap one another ; the partial shadow cast by one linger preventing the No, 1383, vor.. 53] deposit on the plate from becoming so dense as to obscure the presence of the black line. I enclose apari/13/: which shows the presence of the corresponding wltite line very clearly. !\I attention was first culled to the presence of this line on my pictures onjanuaty 28, by Mr. john 'l`. Morris, of this College. I lieve that the prominence of the Hnger-nails is due to the same cause. I have also taken graphs of over-lapping wood, metal, and ivory objects which exhibit the same phenomena." We have received the prints referred to by Mr. Porter, and they entirely bear out his description ol' the appearance presented. For some time past Prof. FitzGemld and Mr. Fred. T. Trouton, at Trinity College, Dublin, have sought evidence of crystalline action, both on transmission and retiection at grazing incidence of Rtintgen rays. 'Though so far this has been with- out success, we learn that they have noticed a marked scattering of the rays in transmission through some substances. The follow- ing nrrangenient is convenient for showing this. “ On a plate of lead, which has a slit cut in it, is placed a sheet of, sity, solid paraffin 2 or 3 m.m. thick, so as to cover one end of the slit; over this is laid a strip of lead-but slightly wider than the slit-so as to just entirely cover the slit. No direct radiation then can pass from a Crookes’ tube, placed vertically over the slit, toasensitivc plate placed behind the lead; but with a lengthened exposure (zo to 30 minutes) with a focus tube, a darkening is found on developing at the end where the paratiin is placed. If the paratiin he then moved to the centre or other end, so as to eliminate accidental eftects, on a ain exposing the darkening action is found to follo\v the parnén. Some darkening always occurs even where there is no solid body. llow much of this is due to successive rellections from the lend sheet and strip, or how much is due to scattering of the rays by air, is not easy to say.” Mr. Dayton C. Miller has obtained some good results at Case School of Applied Science in Cleveland, Ohio, U.S.A., but the exposures be finds necessary are longer than those given by the foremost workers in Great Britain. The tube used by him is spherical in shape, and about five inches in diameter. The coil gives a six-inch spark in air, and is excited by a current ol' about sixty watts, obtntnerl front tifteen cells of storage buttery. The voltage usetl varies front twelve to twenty. With this apparatus antl mower, Mr. Miller says:- “ lI`he bones ofthe Gngers are distinctly shown with exposures of ten seconds, while exposures varying frinn two to ten minutes are regularly uscd in locating bullets and shot in the hand, and in examining injured or deformed hands. :\n excellent picture of a hand and fore-arm, placed diagonally across an rr x 14 plate, has been matic with twenty minutes’ exposure. The entire detail nl' the lettering and design of an a_lu|niuiun1 medal has been taken i|\ Eve minutes. Nunterous interesting surgical cases of fracturetl and diseased arm-bones have been examined with satisfactory results. Photographs of thc chest and head have been made with exposures of one hour in each Case. A surprising nmount of detail is visible. The chest picture shows the shoulder-joint, the collar-hone, the spinal column with its articulations, and a dark streak along its length corresponding to the spinal cord, and eight ribs on each side of the spine. In the region ot' the heart the detail is less con- spicuops, indicating that the heart is ntore opaque than the lung tissue. Mr. W. L. (loodwin, ol' the School of Mining, Kingston, Canada, has sent us the results of experiments made tn deter- mine the relative opacities of vnriuus substances to Riintgen rays. The only details as to the method employed is that the results were obtained “ hy photography with a small Cmokes’ tube similar in shape to a radiotneter, but constructed to show the revolution of a platinum vane covered on one sitle with mica.” The relative opacities thus determined are as follows :~ I. Sor.n>s:- 77a/zrparm/: Fatah... "as, m.m. .....\.t.tmt, cone tin p.nt,, nsphulte, ttlbertite, stnrclt, tlinntontls. Hrirb/ frarrrpparz/:lr Citric acid, jet, anlhracite, amber, natro- lite, caustic potash, caustic soda, borax, soda crystals. Samcwha/ tmm‘pareut.' Silicihed wood, Epsom salts, ser- pentine, staurnlite, stilbite, lazulite, l{2(NH4)PO4, cryo- lire, Mol\r’s salt, analcite, Na2CO.,, borax glass, nitre, Rochelle salt.

616 NATURE [AI’RIL 30, 1896 l Safucmhal 0 ar nf: ltlicn, tnurntaline, wulfenitc, axinite, . M"l”‘ i llelravlour to spincl, calgitd, aragonite, kaolin, NiSU4tNlI,),S(_)4.6ll,(), Lmnpmuid' sp' 8" i C°‘°`"' - i Rii“\B=" “YS- NiSO‘.l{5SO|.6ll,(), &c. _ _Wv _ _g _Y i __ Wi* Gpnquer Roll sulphur, crystal ol' rhomhic sulphur, fluor- ` y g , spar, topaz, beryl, ruby, quartz, NaCl, chalco~pyrite, l`°5O¢r 71120 V85 273 Llllhi 5399" sllf!l"\|Yl955 °P3q‘f¢ I{,(N}I,pA§t),, Il,l{AsO|, l{,FeCy,,, K,Cr,U,, orpmrent, lhfm others In anhydrite, celestine, barite, r _ ' tlns group. _ - N1St)¢. 7ll,0 V95 280 Deep green \About the same Sulphuric acid is as opaque as the satire thickness of sulphur. CoSO,, 7ll,O t'9z 18| I’ink 1' relative opacity. Water is more opaque than parnflin wax. _._ __ _.-.___ A number of crystals ofabout the smnc thickness were photo~ 4\l,U, 4'00 |03 \Vhitc Transparent. graphed on the same plate, and an attempt made to judge of Cr,O, 4'99 153 Green Semi-opaque. their relative transparency with a scale from r tn to, with the l<`e,(), 5-13 |60 ` Hruwn Opaque, following results :- ‘ .__ _-__ _i_.__ _ lllgfl .. 3'42 40 White Trans rent. ll,l\AsO, -- l ZnO 5'47 8| , White Senriixmpaque. 1lflNH|lA5O4~-- 2 lfgO' ll'l3 216 i Red Opaque. N1SO,.(NI{|),SO, 6ll,,O 3 ` I l\lgSO¢.K,SO,.6ll,O,,. 3 _`* W NiSt)‘.K,S(),.6ll,() 3-5 The foregoing figures, conclude the authors, demonstrate the r»1gso,.tNtt,),so,.r.t|,<> ._ 4 zaso,.(N|t.),so,_r.||,o ._ 4 CoSt)|.K,SO).6ll,f) 4 CoSO,.(NII,),SO¢6Il,() 4 lI,(Nl{‘)l"'()4 5 Paraffin wax ._ ro The different values of arsenic and phosphorus in thc iso» mor hous acid arseniatcs and phosplt:-ttes are to be remarked. Tliin sections ofa granite composed principally of quartz and feldspar and of a horrtltlcntlogaltltro were pltotngraphed. ln both cases therfeldspar was found to be distinctly more trans~ parent than tlte other constituents. Protf E. Doelter, ol' (lraz, has conrntunicnted to the Nullvr- rr/irselrs:/iq#/hh: Vzrefn _hir S/r'r?'v'r/ravi' some observations relating to the opacity of dillerent rocks and minerals for the Rontgen rays, and their use as providing a test of the genuine- ness of precious stones. Dr. Doelter Gntls that (I) the opacity does not always increase \\itlt tlte density, although minerals having a specihc gravity gt-eater than 5 are relatively opaque; (2) the complexity of the cltctnicztl constitution of a mineral aflbcts its opacity, bttt no general law of relationship can he enunciated; (3)dimorpl1ous minerals exhibit but slight differ- ences in their behaviour with regard tn the rays in their different formsi (4) in most crystals, the arnmnrt ttf absorption does not depend sensibly on the direction of tlte incident rays; (5) all minerals naturally fall into abottt eight wel|~delined groups, according to their opacity, tlte order being as follows: diamond, corttndttm, talc, quartz, roclosalt, Iceland spar, &c. The diamond is ten times as transparent as r-orumtum, and zoo times as trans iarent as tinfoil. Mr. Ackroyd antl Mr. Il. Il. Knowles have systematically examined the opacity of rt mnnlwr of substances for ltiintgen rays. with a view to tleterrniuing whether it bears any relatiott to molecular weigl1t(_/aurmrl of llte Society of Dyers and Cleaners, April). With this view they have cotnpared tlte isomorphous sulphates, RSO” 7ll2O of the eighth group of metals, iron, nickel, antl cobalt; tlte oxides, RO, of some members ofthe second natttral group, viz. magnesium, zinc, and mercury; the isomorpltous oxides, R,O,, of the metals aluminium, chromium, and iron. In each of these series there are presumably similarly shaped molecules for comparison, and the disturbing factor is the difference of molecular neight. The result of an hour and a halfs exposure showed that the alutninn was practically transparent, the chromium sesquioxide semi-transparent, while the ferric oxide was opaque. ln other words, the opacity of the substance was in some direct relation to the mnlecular weight. There are here marked diflerences with big jumps in molecular weights. The same observation applies to tlte oxides of magnesium, riuc, and mercury. The isomorphous sulphates of iron, nickel, and cobalt are extremely interesting, because of the nenrncss of tlte specilic gravity numbers, and also ul thc ntolccttlnr weights. 'l`he iron compound, with lower specific gravity and molecular weight, a xpertrs to be the least opaque of tln: tltrce, while the nickel and cobalt compounds of nearly the satne specific gravity and molecular weight have approximately the same degree of opacity. The following table correlates these facts with other properties :- No. 1383, vor.. 53] weakness of an unqualified law of density, as the denser oxide of zinc is ntore transparent than the less dense ferric oxide. But they point out that, adopting the legitimate method, which they have initiated, of comparing only compounds with kinship, each of the above bodies conforms to the law of densityas well as of molecular weight in relation to opacity. Ur. A. Sclla and Dr. Q. ltlajorana (Raimi R. Amzd. dn' Lim'rr') describe certain experiments on the influence of Riintgen rays on the sparks produced by the discharge of an induction coil in air. he sparking distance is found to be shortened by the Riintgen rays, this etfect taking place whenever these rays- fall on the positive pole. In this respect thc phenomenon is the reverse of that obtained by llertz with ultra-violet light, the ellbct of which is to lengthen the sparking distance whenever it hills on the negative pole. The authors found that the simul- taneous actions of liontgen rays and ofultra-violet light could be made to neutralise each other by arranging the coil to given. spark of suitable length (in their experiments about 30 mtn.). When the sparking distance was less, the Ilertz eR'ect pre- donrinatetl; nhen the sparking distance exceeded 3o mm., the Riintgen rays had the greater inllucnce. llr. Filippo Cantpanileand Dr. Emilio Stromei contntnnicate to the lt’eml1?anfa 1/e/l` .-lrrarlzr/mr rizlle Srrknzzfrrrhe e mn/emalirhe (Naples) a note on the phosphorescence and the Rkintgen rays in Croukes’ and (icissler’s tubes, The conclusions arrived at are as follows: (l)\Vhen in the circuit of an induction coil,containing tt Crookes’ tube, tt spark is thrown off from the positive pole, the phosphorescence ofthe tttbe and the etticacy ofthe Réintgen radia- tions are augmented. (2) i\s the length of the spark increases the phosphorcscence at Gm increases tn a maximum, and then decreases. (3) If, on the other l1:\nd,ll\c spark is thrown ott” from the negative pole, the phospliorcscence and tlte Riintgen rays are thereby diminishes. The same experirncnlers have also succeeded in obtaining Riintgen rays with nn ordinary Geissler‘stube. These ratliations possessed all the characteristics of those which emanate from a Crookes' tube. Signor E. \`illari, writing in the same journal, considers that the phenomena of discharges in tubes scent to indicate the existence not only of kathodic bttt also of anorlic rays. While the kathodic rays travel in straight lines and produce a negative charge wherever they strike the tttbe, the suggested anodic rays diffuse themselves all rotrnd the anode, and communicate a positive charge to the whole surface of the tube over which they are diffused. The l`undamental character ofthe new rays has led specu- lators to make various surmises as to a possible connection between these radiations and the phenomenon of gravitation, and two lengthy tnetnoirs have been written on the subject by Rudolf l\lewes.‘ ln the second of these the author claims to have proved experimentally that 'ravitation is propagated through the ether with the velocity olilight. Finally, attention tnny profitably be called in this stttnmary to the A iril number of the I’/wrrrir'1/_yr ul' the Physical Society. In the atlutiraltle collection ol abstracts of physical papers there published, will he found concise descriptions of the scope and results of no less than forty papers concerned with Rontgen rays. 1 " |.t.-ta rztenrtetrtnarrrt X-Strahlen" tp... 50; "on rnrr,.naa.a..g§~ t;¥1;wi...xzg1<¢ir au scart-=.t

APRIL 30, 1896] NA TURB 613 RECENT WORK WITH RUNTGEN RA YS. IN our last week’s number, Prof. ]. ]. Thomson brought together and discussed observations of prime importance selected from the mass of material recently published nn Rixntgen nays. As rt supplement to this, and in continuation of the general summaries which have already appeared in NATURE, \ve present the following notes on papers and communications received during the past few days. Prof. Oliver Lodge has sent us the following announcement, dated April zo. “ It has been asserted that the action of X-rays on a film is a Etotographic one, depending on the fluorescence of the glass cking. The truth is that a film on a ferroty e plate is just about as rapid as a similar film on glass. Thick Elms are much better than thin. It may be further interesting to state that if the platinum disk on which the kathode rays inside the bull: are converged is connected to the kathode, it fails to act as a source ; if it he insulated, it acts fairly; while if it is connected tothe anode, it constitutes a vi orous source." It will be remen1bere<¥ that Prof. Riintgen found that “ films can receive the impression as well as ordinary dry plates" (NATURE, january 23, p. 274), but he was doubtful whether the photographic effect was secondary or not. From at number of papers dealing with various properties of Ri:intgen's rays, we learn that Herren V. Novék and O. Sulc (Prague) have ohserved the relative opacity for X-rrtys of tlilTcrcnt xtilmtunccs, lmth simple and compound (Zzksr/tr# #ir I’h_)'.uZ'n/iff/1: C/le///lb, xix. 3). They conclude that the absorbing powers of the chemical element depend on their atomic weight alone, and that the absorbing power of it compound depends only on the atomic weights of the elements ol' which it consists, and not on the complexity of its molecules. It seems probable that the at/:rage atomic weight of a compound aFl'orrls an index of its absorbing power. In the _/e/lair:/ze Z:z?.n‘/zrykfdr Nalzknuirrenrr/tak, Dr. A. Winkel- maun and Dr. R. Straubel (jenn) have investigated the refrac- tiori of Réntgen rays, and by using prisms of various metals, obtain in each case a value of about 1 : 011038 referred to air. They also have measured the reflection produced by a sheet of tintbil, and the relative trans arency of different kimls of glass to Riintgen radiations. All gllasses made with leatl are found to be comparatively opaque. The same \vriters have experimented on the action of fluur-spar in intensifying the actinlc elTects of X-rays, and have found that the best results are obtainable with a coarse powder of the tluor-spar; finer powders producing a less marked effect. This effect is due to iluorescence, the spar emitting radiations whose index of refraction is about t‘48; indi ating rt wave-length of ztgx io`”. The March number bf the _-I./li dc//n /fra/e .Jrraflemrh flu' Li/in-1' contain.; two papers, one by Signor Augusto ltiglii, and the other a joint paper by Drs. A. Fontana and A. Umani (Route), both of which deal with the elfect of lirintgen rays in stopping the action oi Crookes’ ratllometer. The eilect is found tu be purely electrostatical, and to be due tu the electrification of the glass bulb containing the radimueter ; when the bulb is wetted, or electrilication prevented by the interposilion ofa conducting screen, the radiation from a Crookes’ tube does not atTect the radiometer in any way whatever. , . l\Ir. A. W. Isenthal has sent us the following letter. ltpropox of Winlcelmann and Straulzel’s taper. Ile says :-“ It may be of interest tu ynur rearlers to learn that, within the last few weeks, Prof. Dr. Winkelmann and Dr. Straulsel, of Jena University, have been successful in reducing the exposure re- quired for the ‘production of ratliograms to a few seconds only. Acting on the ew directions given, I have rnatle a ten' prelinv inary trials, the result of which is very promising. Iiy simply backing the sensitive plate with a most inexpensive material, I have obtained titir negatives ofthe Bngerbones in about ten seconds, using only a 3-inch spark. As the rays in this methotl have first to pass through the glass of the sensitive plattc, there is a probability of still further reducing the necessary exposure by substituting sensitive films (un Celluloid) for the ordinary photographic plate." With reference to the \\se of fluorescent screens in reducing the time of exposure, we have received the following letter from Dr. II. Van Heurck, of the Botanical Gardens, Antwerp, through I)r. Wynne E. Baxter :- “I notice in your issue of April t6, that Messrs. L. Bleekrode and William Gilfcrd announce that they have been able to reduce the time uf exposure in radiography by the use of No. 1383, vox.. 53] a fluorescent screen. Mr. Basilewslri communicated the same fact to the Paris Acadéniie des Sciences on March 23 last. Allow me, however, to lay claim to priority in this a plication of fluorescent screens, as the same was announced Ey me in various Antwerp journals on March S, and again on the tzth of that month, in the A/male: (Bcfger) de /'har/nank, an extract from which, in pamphlet form, I scnd herewith. You will also find described therein a chemical substance, viz. a newly-dis- covered double fluoride of uranyl and ammonium, with which screens can be made, at a nominal cust, of a luminosity and ofa clearness superior to that of any screen now known to exist.” The combination of a fluorescent screen with a photographic plate was one to which every worker with Riinxgen rays would naturally be led. Prof. M. L. Pupin gavc a description of the combination before the New York Academy of Sciences on March 2. At a meeting ofthe Academy on April 6, reported in Sfienr: of April ln, he described an arrangement of apparatus by means of which it was found possible to produce very strong photographic elfects, “ but not sufficiently strong for penetration through the thigh and the trunk of the human body at reason- ably short exposures and at long enough distances from the tube to obtain the desirable clearness in the pictures of these massive parts. A completely successful application of Ri>ntgen’s beauti- ful discovery to sur ery depends for the present on A successful solution of the prilem just mentioned. Ihave obtained one satisfactory solution with the method which I Erst described behre the Academy on March 2. It consists in placing in con- tuct with the plmtogrnpliic plate n tluuresccul screen, and thus transforming most of the Rtiutgen nuliunce into visible light before it reaches the sensitive film. Pltotngraphs of the hand were thus obtained at a distance of twenty-five feet from the tube with an exposure of halt' an hour. At the distance of four inches the hand can be photographed by an exposure of A few seconds. It was in this manner only that I succeeded in photographing on a single plate the whole chest, shoulders, and neck of my assistant, with an exposure ol seventy minutes and at a distance of three feet between the plate and the tube. The collar-button :md the butt'ons and clasps ofthe trousers and the vest show very strongly through the ribs and the spinal column. This result seems to ‘prove beyond all reaisoimble doubt thc applicability nf ratliograp y to a tuuch larger ticltl in surgery than was expected a few weeks agn," A communication on the same limuch of the subject has been received from Mr. A. A. C. Swinton, under date April 22. We print his letter in full. "The chemical action of the Riintgen rays upon a photo- graphic film may be either a direct action or may bc asecondary effect, due to the fluorescence produced in the support, or in the gelatine and silver hrtnuitlu ul' the lihn itsulli lie this ns it muy, the fnct lhnt au onlinnry pluitugrupltic lihn supported on celluloirl is almost completely tranispurent to the rays, as may easily be proved \vith a cryptoscope, antl also the fact that it is possible to simultaneously impress runny supeniutposed Fthus, show that only a very small l'r.tcti<»n ot" the energy in the rays is utilised uutlcr ordinary circumstances. “ As lung ago as _lanunry 30, in some remarks that I made at the close of Mr. I’orter’s tleuioustrzttinn at University College, I suggested as a means of uture cmupletely utilising the energy in the rays, and thereby shortening the uecessary exposure, the use ol' suitulnlc fluorescent nmterinl upplictl cithcr in the Iorui ol' nscreen behind the plmtogmpliic htm, ur introduced into the substance of the film itself. “Since I first matle this suggestion, I have trierl numerous experiments in the rlirectinn iutlicatetl. These were at first un~ successful owing to thc screens used not having been properly prepared. Sonic weeks ago, ho\vc\'er, on rencniug the experi- ments \vith a screen thickly coated \vith pntassittm platinu- cyunitle and gum, placed llchintl tt ccllulnitl plmtogrnphic hint, I ntinainetl conclusive cvitlencu that lzy this means the necessary exposure coultl he greatly sltrirlumstl, antl that in a less tlegree thc snme result coulrl hc accmnplislrctl hy the employment of n screen thickly coverutl \vith pnwtluretl tltlor-spat". “The chief objection to this tuethotl lies in the tact that it is very difiicul! to avoid granular results. Unless the fluorescent material bein a very fairly tlivitled contlitiun, its grain shows distinctly and mars the detail of the finished picture. The platintrcyanitle docs not work so etliciently when finely powdered as when in moderately coarse crystals, but good results can be olitainerl hy thickly coating a thin cclluloid film with an emulsion nf this salt grountl to tinc powder in collotlion, and using the screen so prepnretl with its collulnitl surhtce: in Contact \vith tht-