The following table compares the refractive indices of the transparent dielectrics with the square roots of the specific inductive capacities. In cases where there is a wide difference u is taken from books on physics; wherever there was a close agreement it was carefully determined by the author, except in the case of paraffin, where the value is that given in Maxwell's "Electricity."

* Messrs. Gibson and Barclay, "Phil. Trans.," 1871, using a method entirely different from mine, obtained K=1.977 for paraffin. Correcting for a slight difference of density, I find that if they had used my paraffin their result would have been 1.9833.

I am not quite certain of the accuracy of this result.

VI. "Researches in Spectrum Analysis in connexion with the Spectrum of the Sun. No. VII."

By J. N. LOCKYER,
F.R.S. Received December 11, 1878. Read December 12.

Discussion of the Working Hypothesis that the so-called Elements are
Compound Bodies.
PART I.

It is known to many Fellows of the Society that I have for the last four years been engaged upon the preparation of a map of the solar spectrum on a large scale, the work including a comparison of the Fraunhofer lines with those visible in the spectrum of the vapour of each of the metallic elements in the electric arc.

To give an idea of the thoroughness of the work, at all events in intention, I may state that the complete spectrum of the sun, on the scale of the working map, will be half a furlong long; that to map the metallic lines and purify the spectra in the manner which has already been described to the Society, more than 100,000 observations have been made and about 2,000 photographs taken.

In some of these photographs we have vapours compared with the sun; in others vapours compared with each other; and others again have been taken to show which lines are long and which are short in the spectra. I may state by way of reminder that the process of purification consisted in this: When, for instance, an impurity of Mn was searched for in Fe, if the longest line of Mn was absent, the short lines must also be absent on the hypothesis that the elements are elementary; if the longest line were present, then the impurity was traced down to the shortest line present.

is that the Elements are Simple Bodies does not include all the Phenomena.

eduction of the photographs of all the metallic elements 39-40-a reduction I began in the early part of the pred which has taken six months, summarised all the obseretallic spectra compared with the Fraunhofer lines accung the whole period of observation. Now this reduction he that the hypothesis that identical lines in different e to impurities is not sufficient. I shall show in detail nt paper the hopeless confusion in which I have been mit nyself on the present occasion to giving tables showypothesis deals with the spectra of iron and titanium. ort-line coincidences between many metals the impurities e been eliminated, or in which the freedom from mutual been demonstrated by the absence of the longest lines.

Evidences of Celestial Dissociation.

ars since I first pointed out that there are many facts

and many trains of thought suggested by solar and stellar physics which point to another hypothesis, namely, that the elements themselves, or at all events some of them, are compound bodies.

In a letter written to M. Dumas, December 3, 1873, and printed in the Comptes Rendus, I thus summarised a memoir which has since appeared in the Philosophical Transactions.

"Il semble que plus une étoile est chaude plus son spectre est simple, et que les éléments métalliques se font voir dans l'ordre de leurs poids atomiques.*

"Ainsi nous avons:

"1. Des étoiles très-brillantes où nous ne voyons que l'hydrogène, en quantité énorme, et le magnésium;

"2. Des étoiles plus froides, comme notre Soleil, où nous trouvons : H+Mg+Na

H+Mg+Na+ Ca, Fe, . . . ;

dans ces étoiles, pas de métalloïdes ;

"3. Des étoiles plus froides encore dans lesquelles tous les éléments métalliques sont ASSOCIÉS, où leurs lignes ne sont plus visibles, et où nous n'avons que les spectres des métalloïdes et des composés.

"4. Plus une étoile est âgée, plus l'hydrogène libre disparaît; sur la terre, nous ne trouvons plus d'hydrogène en liberté.

"Il me semble que ces faits sont les preuves de plusieurs idées émises par vous. J'ai pensé que nous pouvions imaginer une dissociation céleste,' qui continue le travail de nos fourneaux, et que les métalloïdes sont des composés qui sont dissociés par la température solaire, pendant que les éléments métalliques monatomiques, dont les poids atomiques sont les moindres, son précisément ceux qui résistent, même à la température des étoiles les plus chaudes."

Before I proceed further, I should state that while observations of the sun have since shown that calcium should be introduced between hydrogen and magnesium for that luminary, Dr. Huggins' photographs have demonstrated the same fact for the stars, so that in the present state of our knowledge, independent of all hypotheses, the facts may be represented as follows, the symbols indicating the spectrum of which the lines are visible :

*This referred to the old numbers in which Mg=12, Na=23.

Metalloids