SCIENTIFIC SUMMARY. 
107 
character of the general phenomenon above indicated appears from the fact, 
among others, that with rising temperature the friction tone becomes lower. 
The true nature of these tones is at present somewhat obscure. Herr Strou- 
hal offers, with reserve, an interpretation of the facts, for which, however, 
| we must refer to his original paper in the “ Annalen der Physik und Chemie.” 
The Nature of the Elements. — Mr. J. Norman Lockyer read an elaborate 
paper on this subject before the Royal Society on Dec. 12. He discussed 
the evidence obtained from spectroscopic observation of the sun and stars, 
leading to the conclusion that the so-called elements of the chemist are in 
reality compound bodies. The method by which Mr. Lockyer proceeds was 
explained in the last number, while reviewing his recent work “ Studies in 
Spectrum Analysis.” By turning the slit of the spectroscope through 90°, 
and throwing an image of the luminous body on it by means of a lens, he 
is enabled to study the various regions of the heated vapour, and to establish 
the fact that all the lines in the spectrum of the substance volatilised do not 
extend to equal distances from the poles. It is found that the lines fur- 
nished by a particular substance vary not only in length and number, but 
also in brightness and thickness according to the relative amount present. 
About four years ago Mr. Lockyer commenced a map of the spectrum of the 
sun on this principle, with a view of ascertaining* more definitely than has 
hitherto been possible which elements are present in it. A collateral result 
of this important work is to show that the hypothesis that identical lines in 
different spectra are due to impurities is not sufficient ; for he finds short-line 
coincidences between the spectra of many metals in which the freedom from 
mutual impurity has been demonstrated by the absence of the longest lines. 
There are, moreover, many facts which point to another hypothesis, namely 
that the elements themselves, or at all events some of them, are com- 
pound bodies. Thus it seems that the hotter a star the simpler its spectrum, 
for the brightest, such as Sirius, furnish only very thick hydrogen lines 
and a few very thin metallic lines, characteristic of elements of low atomic 
weight ; while the cooler stars, such as our sun, are shown by their spectra 
to contain a much larger number of metallic elements than stars such 
as Sirius, but no non-metallic elements. The coolest stars furnish fluted 
band spectra characteristic of compounds of metallic with non-metallic ele- 
ments. The facts are easily explained if it be supposed that as the tempera- 
ture increases the compounds are first broken up into their constituent 
“ elements” and that these “elements ” then undergo dissociation or decom- 
position into constituents of lower atomic weight. If A contains B as an 
impurity, or as a constituent, in both cases A will have a spectrum of its 
own. B, however, if present as an impurity, will merely add its lines 
according to the amount present, whereas if a constituent of A it will add its 
lines according to the extent to which A is decomposed and B set at liberty. 
So as the temperature increases the spectrum of A will fade if A be a com- 
pound body, whereas it will not fade if A be a true element. Moreover if 
A be a compound body, the longest lines at one temperature will not be the 
longest at another. 
From this point of view, the spectra of calcium, iron, hydrogen, and 
lithium are observed at different temperatures. It is shown that precisely 
