404 



NA TURE 



\_Augitst 24, 1S82 



all multiples of that of hydrogen. This famous hypothesis has 

 gone up and down in the scale of credibility many times during 

 the present century. About seventeen years ago the publication 

 ofStas' new determinations of combining numbers, earrried out 

 on a scale never before attempted, and with all the refinements 

 which the growth of our know ledge could suggest, was thought 

 to have given it its deathblow. But a reaction has set ill 

 si ce that time. The periodic recurrence of the properties 

 of elements with regular additions to the atomic weights, like 

 octaves on a musical scale, put forcibly before us by 

 Mendelejeff, makes it difficult not to think that there is a 

 simple relation between the atomic weights, though there may 

 be causes producing slight perturbations of such a relation. 

 Quite recently a fresh revision of the combining weights has 

 been made on the other side of the Atlantic by I'rof. F. W. 

 Clarke. He has collected all the determinations marie by 

 different observers, ai d after rejecting such as from defective 

 methods were untrustworthy, has applied to the remainder such 

 corrections a> newer excellences have suggested, and then 

 deduced from the corrected numbers the most probable values 

 by the methi ds of the theory of errors. Prof. Clarl-e has done 

 a piece of work of the highest utility, for which chemists must 

 be grateful ; nevertheless he has not carried the revision so far 

 as it might be carried. He has, to begin with, rightly separated 

 the several sets of observation-, and deduced the most probable 

 number for each set by itself, but in combining the various sets 

 for the final determination of the numbers adopted, he has 

 treated the results obtained by different methods as if they were 

 a set of observations all pre umably of equal value, so that the 

 most probable numbers cou'd be deduced by the method of least 

 squares. He has not attempted any discussion of the different 

 ii ethods with a view to an estimate of the lelative values of the 

 results obtained by them, nor made any difference between the 

 values of the figures deduced from operations on the large -cale 

 employed by Stas, and those arrived at 1 n the small scales of 

 other observers. Any sort of handicapping of methods is no 

 doubt a very difficult and delicate operation, and requires more 

 than the judgment of an Admiral Kou-, but without it the 

 question whether the number» adopted are the best obtainable, 

 will always be an open one. It is, however, a very n teworlhy 

 fact that in almost every ca e the numbers deduced from Stas' 

 experiments taken by themselves, coincide very closely with the 

 most probable numbers derived by the method of least squires 

 from the whole of the recorded e timates. On the whole, I'rof. 

 Clarke concludes that I'tout's hypothesis, as modified by Dumas, 

 is still an open question ; tha' is to >ay, his final numbers differ 

 from whole multiples of a common unit by quantities which lie 

 within the limits of errors of observation and experiment. 



Let us turn again to the evidence afforded, by our most power- 

 ful instrument for inspecting the inner constitution of matter, the 

 spectioscope. A few years ago Mr. Lockyer supposed that the 

 coincidence of rays emitted by different chemical elements, par- 

 ticularly when those rays were developed in the spark of a 

 powerful induction-coil and in the high temperatures of the sun 

 and stars, gave evidence of a common e.ement in the composition 

 of the metals which produced the coincident rays. Such an 

 argument could not be drawn from the coincidences unless they 

 were exact, and the identity of the lines could only be tested by 

 means of spectroscopes of great resolving power. By the u-e of 

 the well-known Rutherford gratings, Young, in America, had 

 found that most of the solar lines which had been ascribed to 

 two metals were in reality double, and Prof. Dewar and I, 

 working on the terrestrial elements in the electric arc, had found 

 the actual coincidences to be very few indeed. These observa- 

 tions, even with a Rutherford grating, were delicate enough ; 

 but quite recently M. Fievez, of the Brussels Observatory, has 

 brought to bear on this question a spectroscope of unexampled 

 power. By combining two of the Astronomer-Royal's highly- 

 dispersive half-prisms with a Rutherford grating of 17,296 lines 

 to the inch, he has obtained a dispersion quadruple that of 

 Th 'lion's combination of prisms, bringing this to bear on the 

 sun, he has mapped the solar spectrum from a little below C to 

 somewhere above F on a ^ale one-third greater than that of 

 Vogel's map, and has not only confirmed the work of Young, 

 Dewar, and myself, but has resolved some lines which were not 

 divisible with such dispersive power as we had at command. 

 This result cannot fail to shake our belief, if we have any, in the 

 existence of any common constituent of the chemical elements ; 

 but it does not touch the evidence which the spectroscope affords 

 us 1 hat many of our elements in the state in which we know 



them nun have a very complex molecular structure. I cannot 

 illustrate this point better than by the spectra of two of onr 

 commonest elements, magnesium aid iron. We have good 

 reason to think the molecule of magnesium to be as simple as 

 that of any of our elements, and its spectrum is or.e of the 

 simplest, consisting of a series of triplets which repeat each other 

 111 a regular way and are probably harmonically related, and of a 

 comparatively small number of single lines, of which also 

 may be harmonics. The spectrum of iron, on the other hand, 

 presents thousands of lines distributed irregularly through the 

 whole length, not only of the visible, but of the ultra-violet 

 region. Make what allowance you please for unknown har- 

 monic lelations and for lines no' reversible, which may not be 

 directly due to vibrations of the molecules, we still have a 

 number of vibrations so immense that we can hardly conceive 

 any single molecule capable of all of them, and are almost driven 

 to suppo>e them to be due to a mixture of differing molecules, 

 though as yet we have no independent evidence of this, and no 

 satisfactory proof that any of this mixture is of tbe same kind 

 as occurs in other elements. 



M. Fievez's combination is a great advance in resolving power, 

 but Prof. Rowland, of the Johns Hopkins University, promises 

 us gratings not only exceeding Rutherford's, both in dimensions 

 and accuracy of ruling, but ruled upon curved surfaces, so as to 

 dispense with the use of telescopes and avoid all variations of 

 focussing the different orders of spectra. His instruments, if 

 they come up to the promise he holds out, will enable us to 

 solve many questions which are difficult to answer with our 

 1 resent appliances. 



But to return to the chemical elements : the spectroscope has 

 in the last few years revealed to us everal new metals. I will 

 not venture to say how many ; for when several new metals more 

 or less closely allied are discovered at the same time, the process 

 of sifting out their differences is necessarily a slow one. We 

 cannot tell yet whether any of them are to fill gaps in Men- 

 delejeff 's table, and so add strength to the conviction that 

 there is a natural relation between the atomic weigh s ami 

 the chemical characters of our elementary substan es ; or 

 whether they will add to the embarras ment in which we already 

 find our.-elves with regard to the relations of the ceiinm group of 

 metals; whether we may welcome them as tbe supporters of 

 order, or deprecate their coming as authors of confusion. 

 Granting that the chemical characters of an element are con- 

 nected with its atomic weight, we have, however, no right to 

 assume them to be dependent on that factor al >i 0. \\ by rnav 

 there not be elements which, while they differ as little in atomic 

 weight as do nicl. el and cobalt, are, on the other hand, S' 

 similar to one another in all characters, that their chemical 

 separation may be a matter of the greatest difficulty, anil their 

 difference only distinguishable by the spectroscope ? The spectra 

 may be thought to suggest so much, and how shall we decide the 

 question? At any rate the complications of the spectroscopic 

 problem are such as can only be unravelled by the united efforts 

 of chemists and physicists, and by tbe exercise of extreme 

 caution. 



I cannot dismiss the subject of chemical dynamics without 

 alluding to the ingenious theory by wdiieh the President of the 

 Association has proposed to account for the conservation of solar 

 energy. He supposes planetary space to be | eivaded by an 

 atmosphere which, except where it is condensed by the atti ac- 

 tion of the sun and planets, is in a highly attenuated state. The 

 sun and planets communicate some of their own motion of rota- 

 tion to the atmosphere condensed about them, and he supposes 

 that in this way an action like that of a blowing fan is set up, by 

 which the equatoreal part of the sun's atmo-phere acquires such 

 a velocity as 1 1 stream out to distances beyond the earth's orbit, 

 while an equal quantity of gas is drawn in at the poles to maintain 

 equilibrium The gases thus driven to a distance in planetary 

 space will of course be enormously expanded and highly atten- 

 uated, and in this state Dr. Siemens thinks that such of them as 

 are compound may he decomposed by absorbing the solar radia- 

 tion, and thus the kinetic energy of solar radiation be converted 

 into the potential energy of chemical separation. The sepa- 

 rated elements or partial compounds will, in the circulation pro- 

 duced by the fanlike action of the solar rotation, be carried back 

 to the polar regions of the sun as fuel to maintain his tempera- 

 ture by condensation and re-combination. I will not discuss the 

 mechanical part of this theory farther than to remark that tbe 

 fan-hke action can only be carried on at the expense of the 

 energy of the sun's rotation, which must be in consequence cot.- 



