134 



NATURE 



[Dec. 1 8, 1873 



effected by a shutter, with an opening sliding in front of the 

 slit ; a diagram of its action and form is given. 



The arrangement of the spectroscope, heliostat, &c., for 

 obtaining the sun's light is described. The image of the sun was 

 brought to a focus between the poles of the lamp by an extra 

 lens interposed between the lamp and the heliostat. 



The use of the shutter enables us to compare either two or 

 more spectra upon a single plate, or the solar spectrum may be 

 compared with two metallic spectra, being made to occupy the 

 position between the two. 



III. On the Lines coincident in different Spectra 



The bearing of the former papers on the lengths of the lines 

 of the elements is briefly recapitulated. 



The examination of the various spectra of metals and alloys 

 indicated the great impurity of most of the metals used, and 

 suggested the possibility of the coincidences observed by Thalen 

 and others being explained in the light of former work. 



It is observed that coincidences are particularly numerous in 

 the spectra of iron titanium, and calcium, and that nearly every 

 other solar metallic spectrum has one or more lines coincident 

 with lines of the last element. These coincident lines are, as a 

 rule, very variable in length and intensity in various specimens 

 of the metals in which they occur, and are sometimes altogether 

 absent. 



One of the longest calcium lines, that at wave-length 42263, 

 is also seen in the strontium spectrum as a line of medium length, 

 and 4607 '5, a very long line in strontium, appears in calcium as 

 a short line. Another very long strontium line, 42 15 "3, is as- 

 serted by Thalen to be seen in calcium ; but the author has never 

 seen it till lately, and tlun only in a specimen of calcium known 

 to contain strontium. 



We have here, then, a case of coincident lines, in which the 

 one that is long and bright in one spectrum is short and faint in 

 the other, and a case of a line said to be coincident in two spectra 

 beinCT, though always visible in one, sometimes absent in the 

 other of them, and only appearing in it when the two substances 

 were mixed. The hypothesis of impurity at once explains the 

 whole case, even without the third line, which renders the fact 

 of mixture certain. 



The longest lines of calcium occur in iron, cobalt, nickel, 

 barium, strontium, &c., and the longest lines of iron occur in 

 calcium, strontium, barium, and other metals. 



Other cases are adduced, and the following general statements 

 are hazarded, with a premise that further inquiry may modify 

 them. 



1. If the coincident lines of the metals be considered, those 

 cases are rare in which the lines are of the first order of length in 

 all the spectra to which they are common : those cases are much 

 more frequent in which they are long in one spectrum and shorter 

 in the others. 



2. As a rule, in the instances of those lines of iron, cobalt, 

 nickel, chromium, and manganese which are coincident with 

 lines of calcium, the calcium lines are long, while the lines as 

 they appear in the spectra of the other metals are shorter than 

 the longest lines of those metals. Hence we are justified in as- 

 suming that short lines of iron, cobalt, nickel, chromium, and 

 manganese, coincident with long and strong lines of calcium, are 

 really due to traces of the latter metal occurring in the former as 

 an impurity. 



3. In cases of coincidences of lines found between various 

 spectra the line may be fairly assumed to belong to that one in 

 which it is longest and brightest. 



A description of some photographs of spectra is then given, a 

 photograph of the coincident lines of calcium and strontium 

 being amongst them, and proving that strontium occurs in the 

 sun ; and the section concludes with a brief description of tlie 

 method employed in making the new map, showing lengths and 

 thicknesses, and enumerating coincident lines. This is done 

 thus : papers are pasted on to photographs of the solar spectrum 

 on glass ; the lengths of the lines of the metallic spectrum under 

 examination {e.g. that of iron) are marked on this paper in pro- 

 longation of the solar lines to which they correspond. They are 

 then copied upon a map, and another piece of paper being 

 fixed down, another spectrum is proceeded with in the same 

 way. 



IV. The Preliminary Inquirv into the Existence of Elements 

 in the Sun not previously traced 



The previous researches having shown that the former test for 

 the presence or absence of a metal in the sun, namely, the pre- 



sence or'absence of its brightest or strongest lines in the average 

 solar spectrum, was not conclusive, a preliminary search for 

 other metals was determined on ; and as a guide, Mr. R. J. 

 Friswell was requested to prepare two lists, showing broadly the 

 chief chemical characteristics of the elements traced and not 

 traced in the sun. 



The tables showed that in the main those metals. which had 

 been traced fonned stable compounds with oxygen. 



The author therefore determined to search for the metals 

 which formed strong oxides, but which had not yet been 

 traced. 



The result up to the present time has been that strontium, 

 cadmium, lead, cerium, and uranium would seem with consider- 

 able probability to exist in the solar reversing layer. Should the 

 presence of cerium and uranium be subsequently confirmed, the 

 whole of the iron group of metals will thus have been found in 

 the sun. 



Certain metals forming unstable oxides, such as gold, silver, 

 mercury, &c., were sought for and not found. The same was 

 the case when chlorine, bromine, iodine, &c., were sought by 

 means of their lines produced in tubes by the jar-spark. These 

 elements are distinguishable as a group by forming compounds 

 with hydrogen. 



It is observed that certain elementary and compound gases 

 effect their principal absorption in the most refrangible part of 

 the spectrum when they are rare, and that as they become dense 

 the absorption approaches the less refrangible end ; that the 

 spectra of compounds are banded or columnar, the bands or 

 columns lying at tlie red end of the spectrum ; that the absorp- 

 tion spectra of chlorine, iodine, bromine, is.c., are columnar, and 

 that these are broken up by the spark just as the band spectra of 

 compounds are broken up : and that it is probable that no com- 

 pounds exist in the sun. The following facts, gathered from the 

 work already accomplished by Rutherford and Secchi are 

 stated : — 



There are three classes of stars : — 



1. Those like Sirius, the brightest (and therefore hottest ?) star 

 in the northern sky, their spectra showing only hydrogen lines 

 very thick, and metallic lines exceedingly thin. 



2. A class of stars with a spectrum differing only in degree 

 from those of the class of Sirius, and to this our sun belongs. 



3. A class of stars with columnar or banded spectra indicat- 

 ing the formation of compounds. 



The question is asked whether all the above facts cannot be 

 gi'ouped together in a working hypothesis, which assumes that 

 in the reversing layers of the sun and stars various degrees of 

 " celestial dissociation " are at work which prevents the coming 

 together of the atoms which, at the temperature of the earth, 

 and at all artificial temperatures yet attained here, form the 

 metals, the metalloids, and compounds. 



In other words, the metalloids are regarded as quasi compound 

 bodies when in the state in which we know them ; and it is sup- 

 posed that in the sun the temperature is too great to permit them 

 to exist in that state in the reversing layer, though they may be 

 found at the outer portions of the chromosphere or in the 

 corona. 



It is suggested that if this hypothesis should gain strength 

 from subsequent work, stony meteorites will represent the third 

 class of metalloidal or compound stars, and iron meteorites the 

 other, or metaUic stars. 



The paper concludes as follows : — 



" An interesting physical speculation connected with this 

 working hypothesis is the effect on the period of duration of a 

 star's heat which would be brought about by assuming that the 

 original atoms of which a star is composed are possessed of the 

 increased potential energy of combination \\ hich this hypothesis 

 endows them with. From the earliest phase of a star's life the 

 dissipation of energy would, as it were, bring into play a new 

 supply of heat, and so prolong the star's life. 



" May it not also be, if chemists take up this question, which 

 has arisen from the spectroscopic evidence of what I have before 

 termed the plasticity of the molecules of the metalloids taken as 

 a whole, that much of the power of variation which is at present 

 accorded to metals may be traced home to tlie metalloids ? I 

 need only refer to the fact that, so far as I can learn, all so- 

 called changes of atomicity take place when metalloids are in- 

 volved, and not when the metals alone are in question. 



" As instances of these, I may refer to the tri.atomic combina- 

 tions fonned with cldorine, oxygen, sulphur, &c. in the case of 

 tetrad or hexad metals. May not this be explained by the plas- 

 ticity of the metalloids in question ? 



