Intelligence and Miscellaneous Articles. 24-7 



The light was almost monochromatic, and consisted of a single bright 

 line, which was on the left of the well-known group of lines of cal- 

 cium. By measuring its distance from this group I determined the 

 wave-length of the line, and found it 



X = 5567. 



Besides this line, the intensity of which is relatively very great, I 

 observed, after the slit had been widened, traces of three very faint 

 bands which extended nearly as far as F. Only once, when the lu- 

 minous arc w r as much agitated, owing to undulations which altered 

 its shape, did I see the regions in question momentarily illuminated 

 by some faint spectrum-lines ; yet, from the feeble intensity of these 

 rays, we may still say that the light of the luminous arc is almost 

 monochromatic. 



One circumstance imparts to this observation of the spectrum of 

 the aurora borealis afar greater, I may almost saycosmical, interest. 

 In March of 1867 I observed for a whole week the same line in the 

 zodiacal light, which at that time displayed an extraordinary in- 

 tensity. Finally, on a starlight night, when the whole sky was in 

 some degree phosphorescent, I found traces even in the faint light 

 which proceeded from all parts of the heavens. 



It is a remarkable fact that the line in question does not coincide 

 with any of the known lines in the spectra of simple or of compound 

 gases — at any rate, as far as I have investigated them. 



From what has just been said it follows that an intense northern 

 light, such as can be observed within the polar circle, will probably 

 give a more complex spectrum than that which I have observed. If 

 this be the case, we may also hope that in the future we shall be able 

 to explain more easily the origin of the lines found and the nature of 

 the phenomenon itself. But since I cannot at present give this ex- 

 planation I intend to revert to it on a future occasion. — Poggendorff's 

 Annalen, May 1869. 



ON THE THERMAL ENERGY OF MOLECULAR VORTICES. BY W. J. 

 MACQUORN RANKINEj C.E._, LL.D.j F.R.SS. LOND. & EDINB. ETC.* 



In a previous paper, presented to the Royal Society of Edinburgh 

 in December 1849, and read on the 5th of February 1850 (Transac- 

 tions, vol. xx.), the author deduced the principles of thermodynamics, 

 and various properties of elastic fluids, from the hypothesis of mole- 

 cular vortices, under certain special suppositions as to the figure and 

 arrangement of the vortices, and as to the properties of the matter 

 which moves in them. In subsequent papers he showed how the 

 hypothesis might be simplified by dispensing with some of the special 

 suppositions. In the present paper he makes further progress in the 

 same direction, and shows how the general equation of thermody- 

 namics and other propositions are deduced from the hypothesis of 

 molecular vortices when freed from all special suppositions as to the 

 figure and arrangement of the vortices, and the properties of the 

 matter that moves in them, and reduced simply to the following 

 form — that thermometric heat consists in a motion of the particles of 



* Communicated by the Author, having been read before the Royal 

 Society of Edinburgh, May .31, 1869. 



