562 REPOET— 1886. 



may consider the conclusion arrived at by Herscliel, and pursued by Clerk -Maxwell, 

 that atoms hear the impress of manulactured articles. Let us look a little more 

 closely at this view. A manufactured article may well be supposed to involve a 

 manufacturer. But it does somethino^ more : it implies certain!}' a raw material, 

 and probably, though not certainly, the existence of by-products, residues, paralei- 

 pomena. AVhat or where is here the raw material ? Can we detect any form of 

 matter which bears to the chemical elements a relation like that of a raw material 

 to the finished product — like that, say, of coal-taj' to alizarin ? Or can we recognise 

 any elementary bodies which seem like waste or refuse ? Or are all the elements, 

 according to the common view coequals ? To these questions no direct answer is 

 as yet forthcoming. 



And this leads us up to a hypothesis which, if capable of full demonstration, 

 would show us that the accepted elements are not coequal, but have been formed 

 by a process of expansion or evolution. I refer to the well-known hypothesis of 

 Prout, which regards the atomic weights of the elements as multiples, by a series 

 of whole numbers, of uuity = the atomic weight of hydrogen. Everyone is aware 

 that the recent more accurate determinations of the atomic weights of different 

 elements do not by any means bring them into close harmony with the values 

 which Prout's law would require. Still in no small number of cases the actual 

 atomic weights approach so closely to those which the hij-[3othesis demands that 

 we can scarcely regard the coincidence as accidental. Accordingly, not a few 

 chemists of admitted eminence consider that we have here an expression of the 

 truth, masked by some residual or collateral phenomena which we have not yet 

 succeeded in eliminating. 



The original calculations on which the most accurate numbers for the atomic 

 ■weights are founded have recently been recalculated by Mr. F. W. Clarke. In 

 bis concluding remarks, speaking of Prout's law, Mr. Clarke says that 'none of 

 the seeming e.xceptious are inexplicable. In short, admitting half-multiples as 

 legitimate, it is more probable that the few apparent exceptions are due to un- 

 detected constant errors than that the great number of close agreements should be 

 xaerely accidental. I began this recalculation of the atomic weights with a strong 

 prejudice against Prout's hypothesis, but the facts as they came before me have 

 forced me to give it a very respectful consideration.' 



But if the evidence in favour of Prout's hypothesis in its original guise is 

 deemed insufficient, may not Mr. Clarke's suggestion of half-multiples place it upon 

 an entirely new basis? Suppose that the unit of the scale, the body whose atomic 

 weight, if multiplied by a series of whole numbers, gives the atomic weights of the 

 remaining elements, is not hydrogen, but some element of still lower atomic weight ? 

 We are here at once reminded of helium — an element purely hypothetical as far as 

 our Earth is concerned, but supposed by many authorities, on the faith of spectro- 

 scopic observations, to exist in the sun and in other stellar bodies. INIost solar 

 eruptions present merely the characteristic lines of hydrogen C, F, and H, and 

 along with them one particular line whicli at first was classed in the sodium group, 

 but which is a little more refrangible, and is designated by the s^-mbol D^. Ac- 

 cording to Mr. Norman Lockyer and the late Father Secchi, this ray undergoes 

 modifications not comparable to those afl'ecting other rays of the chromosphere. 

 In the corresponding region of the spectrum no dark ray has been observed. That 

 the accompanying lines C, F, and H pertain to hydrogen is evident ; and as J), 

 has never Ijeen obtained in any other spectrimi, it is supposed to belong to a body 

 foreign to our Earth, though existing in abundance in the chromosphere of the sun. 

 To this hypothetical body the name helium is assigned. 



In an able memoir on this subject, read before the Academy of Brussels, the 

 Abbe E. Sp^e showsthat,if helium exists, it enjoys two very remarkable properties. 

 Its spectrum consists of a single ra}', and its vapour possesses no absorbent power. 

 The simple single ray, though I believe unexampled, is by no means an impossible 

 phenomenon, and indicates a remarkable simplicity of molecular constitution. The 

 non-absorbent property of its vapour seems to be a serious objection to a general 

 physical law. Professor Tyndall has demonstrated that the absorptive power 



