476 



NA TURE 



[March i6, 1905 



the helium spectrum is probably none other than the same 

 line. They can, however, assign no reason for its appear- 

 ance in only one of the numerous photographs of the 

 helium spectrum taken at Kensington. 



" Note on the Spectrum of yu Centauri." By Sir Norman 

 Lockyer, K.C.B., F.R.S., and F. E. Baxandall, 

 A.R.C.Sc. 



In this note the authors give an analysis of some of the 

 bright lines in the spectrum of /i Centauri. This star not 

 being available at Kensington, an excellent reproduction 

 by Prof. Pickering was used as a basis for the analysis. 



The chief bright lines belong to hydrogen, as Pickering 

 and other observers have pointed out. The minor bright 

 lines, however, have hitherto had no origin suggested for 

 them. In this note it is shown that the most marked of 

 the minor bright lines agree very closely in position with 

 the strongest enhanced lines of iron, and the authors con- 

 clude that the stellar and terrestrial lines are probably 

 identical in origin. It is pointed out that the same lines are 

 conspicuous in the spectra of Nov;e in their earlier stages. 



" The Arc Spectrum of .Scandium and its Relation to 

 Celestial Spectra." Bv Sir Norman Lockyer, K.C.B., 

 F.R.S., and F. E. Baxandall, A.R.C.Sc. 



In this paper a record is given ol the lines in the arc 

 spectrum of the rare clement scandium between X 3900 and 

 X 5720. The photograph used for reduction was taken with 

 a large Rowland concave grating, having a ruled surface 

 of 5^X2 inches (143X5 cm.) and a radius of 21 feet 6 

 inches. The scale of the photograph is such that the 

 distance between K and D is 30] inches, or 77 cm. This 

 is equivalent to 26 tenth-metres per millimetre. 



hx\ analysis of the lines is given with regard to their 

 appearance in the Fraunhoferic spectrum. It is shown that 

 nearly all the stronger lines occur as solar lines, but the 

 great majority of the lines weaker than intensity 6 

 (maximum intensity 10) are mi.ssing from the solar spectrum. 



Short analyses are also given of the relation of the 

 scandium arc lines to the lines in the spectra of the 

 chromosphere, sun-spots, and stars. The strongest scan- 

 dium lines are shown to be specially prominent in the 

 chromospheric spectrum, the same lines being conspicuous 

 in stellar spectra of the Polarian type {e.g. y Cygni). In 

 the higher stellar type Cygnian (a Cygni), the strongest 

 scandium lines are present, but only weak. At the still 

 higher stages of stellar spectra the scandium lines are 

 lacking. 



With regard to sun- spot spectra, the only solar-scandium 

 line (X 5672-047) given by Rowland in the region F to D, 

 is found to be nearly always well affected, and it often 

 occurs amongst the twelve most widened lines recorded at 

 Kensington in spot spectra. 



■' On Europium and lis Lltra-violet Spectrum " : Sir 

 William Crookes, F'.R.S. 



Exner and Haschek have measured the wave- 

 lengths of the europium lines ' from material sup- 

 plied by DemarQay. -A comparison of their lines with 

 the present author's shows that the material was by 

 no means pure. Urbain's europia is not quite so free from 

 impurities as his gadolinia. The author has been able to 

 detect in his photographs the following lines : — Gadolinium 

 is represented by very faint lines at 3450.55, 3481.91), 3585.10, 

 3646-36, 3654-79. 3656.32, 3664-76, 3697PO. 369989, 374362, 

 3768-52, 3796.58, 3805.70, 3850.83, 3851.16, 4050.0S, 4225.33. 

 Yttrium is represented by the line at 3774.51, lanthanum by 

 the line at 3988.66, and calcium by the two lines at 3933.825 

 and 3968.625. 



February 9 and February 23. — " Phosphorescence caused 

 by the Beta and Gamma Rays of Radium." Bv G. T. 

 Beilby. Communicated by Prof. Larmor, Sec. R.S. Part 

 i. read February 9, part ii. read February 23. 



The conclusions arrived at in these papers mav be sum- 

 marised as follows : — 



(i) Certain types of phosphorescence are due to the 

 molecular movement or displacement which is produced by 

 heat, by mechanical stresses, or by radiant energy. 



(2) Certain other types are distinguished by their appear- 

 ance in three stages, called here primary, secondary, and 



' " Wellenl.HnBen.Tabellen fiir Spektr.ilanalytischc Untersuchungen," 

 F. Deiiticke. (lleipzig and Vienna, 1902.) 



NO. 1846, VOL. 71] 



revived phosphorescence. These can be explained as due to 

 atomic changes in which chemical affinity is the controlling 

 factor. 



(3) The phenomena of this type appear to support thi 

 view that a species of electrolysis occurs in solids exposed to 

 the /3 or kathode rays ; that the products of electrolysis are 

 insulated from each other, as in a viscous electrolyte ; and 

 that it is the breaking down of this insulation with the 

 re-combination of the ions which causes revived phosphor- 

 escence. 



When the canary-yellow crystals of barium platinocyanide- 

 are exposed to the h and 7 rays for some hours, they turr« 

 red, and their phosphorescence in the rays falls to 8 per cent, 

 of its original value. Neither the colour nor the phosphor- 

 escence is restored by exposure to sunlight or to diffused 

 daylight. The only way completely to restore these qualities 

 is to dissolve the salt in water and re-crystallise it. In this 

 way the reddened salt is completely re-converted into the 

 yellow form, and there are no signs that the reddening has 

 been associated with any permanent chemical change. The 

 possible physical changes were, therefore, investigated. 

 When the crystalline structure of the yellow salt is impaired, 

 either by mechanical flowing or by dehydration by heat, 

 there is a very conspicuous colour change, the canary-yellow 

 giving place to an intense brick-red colour, while the phos- 

 phorescence in the radium rays falls to 2 per cent, of its 

 original value. By solution and crystallisation these 

 amorphous forms are restored to the yellow crystalline state 

 with its full phosphorescent value. The effects produced by 

 the /3 rays are, therefore, closely analogous to those produced 

 by the change from the crystalline to the amorphous state. 

 In the light of the author's earlier observations on the 

 phase changes .AZ^C in metals and salts, it was to be 

 expected that the change C — -.\, produced by mechanical 

 flow, would be reversed by raising the temperature of the 

 substance to the stability point of the .A phase. Making due 

 allowance for the difficulty caused by the presence of water 

 of crystallisation and its partial loss on heating the salt, it 

 was found that the change .\ — -C could be brought about 

 in the mechanically-flowed salt at a temperature of about 

 90°, the colour being thereby changed from red to yellow, and 

 the phosphorescence raised from 2 per cent, to 33 per cent, 

 of its original value. It was found that the crystals reddened 

 bv the rays could also be partially restored to their former 

 condition of colour and phosphorescence by quickly heating 

 them in a sealed capillary tube to about 120°. By this treat- 

 ment the phosphorescence was raised from 8 per cent, to 

 33 per cent, of its original value in the yellow crystals. 

 The analogy between the phase changes caused by 

 mechanical flow and the change which results from ex- 

 posure to the j8 rays is thus complete, and it is concluded 

 that the over-stimulation to which the vibrating mclecules 

 of the platinocyanide crystals are subjected under the action 

 of the fl rays during the preliminary stage of bright phos- 

 phorescence results in a state analogous to that of elastic 

 fatigue in vibrating metal wires or glass fibres. Up to a 

 certain point, this fatigue may be recovered from, that is- 

 to say, if the relative displacement of the molecules from 

 their proper crystalline relations has not passed beyond a 

 certain stage ; but beyond this stage there is no power of 

 self-recovery, and heat is necessary to endow the molecules 

 with freedom of movement sufficient to enable them to return 

 to their crystalline positions. The final stage of permanent 

 fatigue or over-strain in the salt corresponds with the 

 amorphous condition which results from mechanically-pro- 

 duced flow. The comparalive instability of the crystalline 

 structure in this salt has thus been the means of directing 

 attention to the part which may be played by physical 

 structure in phosphorescence. But the persistence of phos- 

 phorescence, even in the amorphous state, gives an equally 

 clear indication that a more general explanation of these 

 phenomena is still needed. 



This further explanation was reached by a study of the 

 action of the /3 and 7 rays on quartz, glass, calcspar, and 

 the haloid salts of potassium. In these substances, in 

 addition to a primary phosphorescence, the rays produce 

 certain well-marked loloration effects ; quartz is turned 

 brown, calcspar faint yellow, glass purple or brow^n, 

 potassium chloride reddish-violet, and bromide and iodide 

 blue to green. Further, whether the coloration lasts for 

 months or only for a few moments, it is found that phosphor- 



;i 



