392 



NATURE 



{Azigiisi 25, 



Huggins writes : '—"The spectrum of Vega may be taken con- 

 veniently as typical of the whole clas, of white stars, so that the 

 dibtinctive features of the other stars of this class may be regarded 

 as modifications or departures from this coraoion typical form." 

 He then adds : " There are principally three directions in which 

 changes take place"; one of these consists "in the presence 

 or absence of K, and if present, in its breadth and intensify 

 relative to H." He goes on, "One of these modifications, 

 which possess great suggcativeness, consists of the absence, or 

 difference of character presented by the line K. In all the stars 

 of this class this line ii either absent or is very thin as compared 

 with its appearance in the solar spectrum, at the same time that 

 H remains very broad and intense. In the spectrum of Arcturus, 

 a star which belongs to anothei- class which includes our sun, 

 this line K has passed beyond the co.idition in which it occurs 

 in the solar spectrum, and even exceeds the solar K in breadth 

 and intensity." Arcturus is given in the lower part of the dia- 

 gram, and it will be seen tliat there K is relatively thicker than 

 H ; and also that with this relative increase in the thickness of K 

 we get a considerable complexity of spectrum, very much more 

 approaclring the solar spectrum in the number of lines that we 

 have to contend wfith. But at the same time I should point out 

 that the positions of these lines vary from the positions of lines in 

 the solar spectrum. " The spectra of these stars," Dr. Huggins 

 continues, "may therefore be arranged in a continuous series, 

 in which first we find this line to be absent. Then it appears as 

 an exceedingly thin line. We then pass to another stage in which 

 it is distinct and defined at the edges ; in the solar spectrum it 

 becomes broad and winged, and lastly in Arcturus there is further 

 progress in the same direction, and the line, now a broad band, 

 exceeds in intensity H." Absolute continuity we see in the story 

 which Dr. Huggins brings us with reference to this concrete 

 case of h' and K in the details and in general. Well might 

 Dr. Huggins ask after this : "Do these modifications not repre- 

 sent some of the stages through which our sun has passed ? j' 

 In another part of his paper he uses the term "life changes." 

 Now the life of a star is its temperature, and all these changes 

 must have been produced by the running down of temperature, 

 and I think the simplest view to take, limiting ourselves to the 

 cojcrete change of H and K, is that the substance which pro- 

 duces K has been formed at the expense of the substance which 

 produced H, and the reason that we see these two lines in 

 calcium when a high temperature is employed is that we reveal 

 the preence of these true root-forms. There may be very many 

 more difficult explanations, but that I think is the simplest one 

 to which one is driven by the logic of facts. 



The appeal to the stars, then, I think, amply justifies the pre- 

 diction which I based upon the comparison of solar with terres- 

 trial phenomena, and, therefore, helps to show that the basis on 

 which those predictions were founded had at all events some 

 little glimmering of truth about it. I think also that it increases 

 the dissociation stages through which we must assume the vapours 

 of our so-called elements to pass when higher temperatures are 

 employed in succession. 



So much then for the tests which we have been able to apply 

 to these views by means of Dr. Huggins' remarkably beautiful 

 researches. , , , , 



The wide departure of stars hotter presumably than the sun 

 (taking the centre of gravity of the absorption, so to speak, as 

 the indication of temperature) from the solar type shows that 

 there is much more work to be done in this field. The success 

 of my former prediction emboldens me to make another one. 

 It will in all probability be found that the remaining thick lines in 

 stars of the Sirius type are represented in many cases by the lines 

 brightened in solar prominences. 



Tests afforded by the Phenomena of Fluted Spectra 

 So far vi'e have dealt with line spectra, but we must not 

 limit ourselves to a consideraticm of this class of spectra if v\ e 

 wish to test this view to the very bottom, as it is our bounden 

 duty to do. We have therefore to ask ourselves the question 

 with reference to other regions of spectrum analysis beyond that 

 particular part which we have been discussing : Is the evidence 

 to be got from those other regions the same? Does it tend in 

 the same direction as the evidence which has been supplied from 

 the consideration of the highest possible temperature in our coils 

 and in the sun ? I have no hesitation in saying that, so far as I 

 know, the evidence is absolutely strengthened by a consideration 

 of the low temperature phenomena observed spectrosco ically. 

 ' Phil. Trans., i83o. 



In fact the vieiv was started very many years ago by observa- 

 tions at much lower temperalures than those we have been con- 

 sidering. Pliicker and Hittorf, who worked at spectrum analysis 

 before Kirchhofif and Bunsen, n ere bound to acknowledge that 

 some of the substances with which they dealt had really two 

 distinct spectra, which they called spectra of the first order, 

 and spectra of the second order, which spectra changed as the 

 temperature they employed changed ; and although they came 

 to the conclusion that these simply represented allotropic condi- 

 tions, not molecular dissociation, I think when one comes to 

 inquire into the subject thoroughly, one will find there cannot be 

 any very great difference between thosC two considerations. In 

 fact the question of double spectra, which has been fought 

 for many years, but which I think is now nearly at rest, was 

 started by the observation of Pliicker and Hittorf. Of course 

 the view they put forward was objected to very tirongly, and 

 was met by the assertion that they were misled by impurities in 

 the substances which they experimented on. For instance, they 

 found a second spectrum for hydrogen ; this second spectrum, 

 which had a very special character of its own, was referred to 

 acetylene. Soon after, a part of the carbon spectrum which 

 was entirely different from the second spectrum of hydrogen, 

 was referred to acetylene. So that those gentlemen who saw in 

 these phenomena nothing but impurities were perfectly content 

 to give an explanation which would be quite right, provided 

 hydrogen and carbon could only be supposed to have one spec- 

 trum ; the impurity acetylene having two. Later work has 

 shown that it is too coarse a view to think that the Anted spectra 

 which represent the spectra of the first order of Pliicker really 

 represent the vibration of one molecule in the same way that the 

 line-spectra were supposed to do. Evidence has been accumu- 

 lated which indicates that in some cases where we get three or 

 four flutings, those three or four flutings which can be seen one 

 by one are inversely inten ified, in precisely the same way that 

 various lines can be seen one by one, or almost one by one, and 

 inversely intensified. It seems as if even flutings cannot be con- 

 sidered to be simply due to the result of one special kind of 

 allotropism, but probably represent several. 



Let me give a figure or two to repre-ent this point. 

 An application of the principles referred to in Figs. 32 and 

 33 will readily enable us to understand that a substance may 

 give us a particular fluting at the lowest temperature, represented 

 by the fnrnace C, a different fluting in the furnace B, and finally 

 a line at the highest temperature afforded by the furnace A, as 

 shown in Fig. 44, and that at intermediate temperatures its 

 spectrum may consist of mixtures in varying proportions of each 

 of these cons' ituents, and it will also be seen that the line pro- 

 duced by the highest temperature can never be seen together 

 with the lowest temperature fluting, unle-s the fluting produce.! 

 by the intermediate temperature is present also. Fig. 45 shows 

 the facts actuiUy observed when the spectru n of carbon is pho- 

 tographed under various conditions of temperature. 



'The results are strikingly suggestive, as we have a compound 

 origin to the two sets of flutings shown. 



But there is a lower region yet, a region in which much work 

 has been done which seems to show that before the substance is 

 fit to give us flutings, that it can still record for us— in a 

 very feeble sort of way — it can yet record for us its vibra- 

 tions by alisorption at one end of the spectrum or at the other, so 

 that the story of simpUfication is really intensified when we leave 

 the high temperature spectrum, and it seems as if the first effect 

 produced by the action of heat on any substance is to give us 

 general absorption wliich breaks up into abs irption in the red 

 and absorption in the blue, and then we get a series of flutings 

 more or less complex according to the temperature of the body ; 

 and then when we have passed from this sta:^e we get the series 

 of line spectra to which I have drawn attention. Again, in 

 passing from a low temperaure to a high temperature, so far as I 

 can see there is absolutely no break, nor is there any difference 

 of kind that we are acquainted \\ith in the passage from a com- 

 pound body and the passage from a known form of, let us say, 

 gold or silver, at a low temperature, to that same substance at 

 a higher temperature. 



If we assume that these various spectra are really due to dif- 

 ferent molecular aggregations, we shall have the following series, 

 going from the more simple to the more complex : — 



stages of complexity \ Liae-spectra. 



molecule J 



Second stages Channelled space or fluted spectra. 



First 

 of 



