414 



NATURE 



{Sept. 2, 1880 



The effects of change of temperature on the character of 

 spectra is very well illustrated by an experiment of M. 

 Wiedemann with mixtures of mercury with hydrogen or nitrogen 

 in a Geissler's tube. At the ordinary temperature of the air 

 the spectrum of hydrogen or nitrogen was obtained alone ; but 

 on heating the lube in an air-bath the lines of mercury appeared 

 and became brighter as the temperature rose, and at the same 

 time tlie hydrogen lines disappeared in the wider portion of the 

 tube and at the electrodes. The liydrogen or nitrogen lines 

 disappeared first from the positive electrode and in the luminous 

 tuft, and as the temperature rose disappeared altogether. With 

 nitrogen in a particular experiment, up to 100° C, the nitrogen 

 lines were seen throughout tlie tube, but from ioo° to 230" the 

 nitrogen lines appear towards the negative pole, and the mercury 

 lines are less bright at the negative than at the positive pole, while 

 at about 230' C. no nitrogen lines appear. The experiments of 

 Roscoe and Schuster, of Lockyer and other observer-, with potas- 

 sium, sodium, and other metalloids in vacuum tubes, from which 

 hydrogen is pumped by a Sprengel pump, also show great changes 

 in the molecular condition of the mixture contained in the tubes 

 when they are heated to different temperatures. The changes of 

 colour in the tube are accompanied by changes in the spectrum. 

 Thus, Lockyer finds that when potassium is placed in the bottom 

 of the tube, and the spark passes in the upper part of it, as the 

 exhaustion proceeds and the tube is slightly heated, the hydrogen 

 lines disappear, and the red potassium line makes its appearance ; 

 then as the temperature is increased, the red line disappears, 

 and three lines in the yellowish-green make their appearance, 

 accompanied by a change in the colour of the tube, and 'at a 

 higher temperature, and with a Leydeu jar joined to a secondary 

 circuit of the induction coil, the gas in the tube becomes of a 

 dull red colour, and with this change a strong line comes out in 

 the spectrum, more refrangible than the usual red potassium line. 

 Ill this case, on varying the conditions, we get a variation in the 

 character of the spectrum, and the colours and spectra are 

 different in different parts of the tube. In Lockyer's experi- 

 ments, at the temperature of the arc obtained from a Siemens' 

 dynamo-machine, great differences appear in different parts of 

 the arc : for instance, with carbon poles in the presence of 

 calcium, the band spectrum of carbon, or the carbon fluting^ 

 and the lines of calcium, some of them reversed, are seen 

 separated in the same way as mercury and hydrogen, the carbon 

 spectrum appearing near one pole and the calcium near the other, 

 the lines which are strongest near that pole being reversed or 

 absorbed by the quantity of calcium vapour surrounding it. On 

 introducing a metal into the arc, lines appear which are of 

 different intensities at different distances from the poles, others 

 are strong at one pole and entirely absent at or near the other, 

 while some lines appear as broad as half-spindles in the middle 

 of the arc, but are not present near the poles. Thus, the blue 

 line of calcium is visible alone at one pole, the H and K line 

 without the blue lines at the other. 



We may prob.ably regard these effects as the result, not of 

 temperature alone, but must take into account that we have 

 powerful electric currents which will act unequally on the mole- 

 cules of different bodies according as they are more or less 

 electro-positive. It would seem that we have here something 

 analogous to the segregation which is observed in the melting of 

 certain alloys to which I have already referred. 

 ■ The abundance of material in some parts of the arc surround- 

 ing the central portion of it gives rise to reversal of the principal 

 lines in varying thicknesses over the arc and poles, so that bright 

 lines appear without reversal in some regions, and reversals or 

 absorption lines without bright lines in others. The introduc- 

 tion of a substance into the arc gives rise to a flame of great 

 complexity with regard to colour and concentric envelopes, and 

 the spectra of these flames differ in different parts of the arc. 

 Thus in a photograph of the flame given by manganese, the 

 Jine at wave-length 4234-5 occurs without the triplet near 4030, 

 ivhile in another the triplet is present witliout the line 4234*5. 



The lines which are reversed most readily in the arc are gene- 

 rally those the absorption of which is most developed in the 

 flame ; thus the manganese triplet in tlie violet is reversed in the 

 flame, and the blue calcium line is often seen widened when tlie 

 H and K lines of calcium are not seen at all. In consequence 

 of the numerous changes in spectra at different temperatures, 

 Mr. Lockyer has advanced the idea that the molecules of ele- 

 mentary matter are continually being more and more broken up 

 as their temperature is increased, and has put forward the hypo- 

 thesis that the chemical elements with which we are acquainted 



are not simple bodies, but are themselves compounds of some 

 other more smiple substances. This theory is founded on Mr. 

 Lockyer's comparisons of spectra and the maps of Angstrom, 

 Thalen, Young, and others, in which there are coincidences of 

 many of the short lines of the spectra of different substances. 

 These short lines are termed basic lines, since they appear to be 

 common to two or more substance?. They appear at the highest 

 temperatures when the longest lines of those substances . and 

 those which are considered the test of their presence are entirely 

 absent. 



Mr. Lockyer draws a distinction between weak lines, which 

 are basic, i.e. which would permanently exist at a higher tem- 

 perature in a more elementary stage, and other weak or short 

 lines which would be more strongly present at a lower tempera- 

 ture, in a more complex stage of the molecules. Thus, in 

 lithium, the red line is a low temperature line, and the yellow 

 is feeble ; at a higher temperature, the red line is weak, the 

 yellow comes out more strongly, and the blue line appears ; at 

 a higher temperature still, the red line disappears, and the 

 yellow dies away ; whilst at the temperature of the sun the 

 violet lithium line is the only one which comes out strongly. 

 These effects are studied by first producing the spectrum of the 

 substance in the Bunsen flames, and observing the changes which 

 are produced on passing a spark through the flame ; thus, in 

 magnesium, a wide triplet or set of three lines (5209'8, b' and 

 b'-') IS changed into a narrow triplet (b', b-, and b^) of the same 

 character. We have here what some observers regard as a re- 

 currence of the same harmonic relation of the vibrations of the 

 same body at a higher temperature. 



If the so-called elements are compounds, they must have been 

 formed at a very high temperature, and as higher and higher 

 temperatures are reached the dissociation of these compound 

 bodies will be effected, and the new line spectra, the real basic 

 lines of those substances which show coincidences, \\\\\ make 

 their appearance a? short lines in the spectra. In accordance 

 with this view, Mr. Lockyer holds that the different layers of 

 the solar atmosphere may be regarded as a series of furnaces, on 

 the hottest of which. A, we have the most elementary forms of 

 matter capable of existing only in its uncombined state ; at a 

 higher and cooler level, B, this form of matter may form a com- 

 pound body, and may no longer exist in a free state at the lower 

 temperature ; as the cooler and cooler levels, C, D, and E, 

 are reached, the sulistances become more and more complex and 

 form different combinations, and their spectra become altered at 

 every stage. Since the successive layers are not at rest, but in 

 a state of disturbance, we may get them somewhat mixed, and 

 the lines at the cooler levels D and E may be associated with the 

 lines of the hotter levels ; these would be basic or coincident 

 lines in the spectra of two different compounds which exist at 

 the cooler levels D and E. We might even get lines which are 

 not present in the hottest furnace A coming into existence as the 

 lines of compounds in B or C, and then extending among the 

 lines belonging to more complex compounds which can only 

 exist at a lower temperature, when they might be present as 

 coincident weak lines in the spectra of several compound bodies. 

 Thus Mr. Lockyer regards the calcium lines li and K of the 

 solar spectrum as evidence of difterent molecular groupings of 

 more elementary bodies. In the electric arc with a weak current 

 the single line 4226 of calcium, which is easily reversed, is much 

 thicker than the two lines H and K ; but the three lines are 

 equally thick with a stronger current and are all reversed. With 

 a spark from a large coil and using a condenser the line 4226 

 disappears, and H and K are strong lines. In the sun, the 

 absorption bands H and K are very broad, but the liand 4226 

 is weak. Prof. Young, in his observation of the lines of the 

 chromosphere, finds that H and K are strongly reversed in every 

 important spot and in solar storms ; but the line 4226, so 

 prominent • in the arc, was only observed three times in the 

 chromosphere. 



One of the most interesting features among the most recent 

 researches in spectrum analysis is the existence of rhythm in 

 the spectra of bodies, as has been shown by MM. Mascart, Cornu, 

 and others, such as the occurrence and repetition of sets of lines, 

 doublets, and triplets in the spectra of different substances and 

 indiflerent parts of the spectrum of the same body. Professors 

 Liveing and Dewar, using the reversed lines in some cases for 

 the more acccurate determination of wave-lengths, have traced 

 out the rhythmical character in the spectra of sodium, potassium, 

 and lithium. They show that the lines of sodium and potassium 

 form groups of four lines each, which recur in a regular sequence, 



