70 Royal Society : — 



When we examine the means for the separate years, we find 





Mean Lunar . 



Disturbance. 



Ratio of range of 











diurnal varia- 





/ 





Ratio to 1856. 



tion to 1856. 



1854 . 



. .. =0-320 



• • 



1-18 .. 



1-27 



1855 . 



0-295 



. , 



1-08 .. 



.. 1-31 



185G . 



0-272 



• • 



1-00 ., 



1-00 



1857 . 



0-326 



• • 



1-20 .. 



1-28 



1858 , 



0-379 



• * 



1-39 .. 



1-41 



1859 . 



0-453 



• • 



1-67 .. 



1-59 



I have not at hand the mean solar disturbances for each year, and 

 cannot therefore compare the two ; it will appear, however, from a 

 comparison with the ranges of the solar diurnal variation (which are 

 known to follow nearly the same law as the law of mean disturbance), 

 that the mean lunar disturbance obeys the same law as the mean solar 

 disturbance, and that the former is probably dependent upon the 

 latter. 



" Experimental Researches on the Functions of the Vagus and the 

 Cervical Sympathetic Nerves in Man." By Augustus Waller, M.D., 

 F.R.S. 



" On the Double Tangents of a Curve of the Fourth Order." By 

 Arthur Cayley, Esq., F.R.S. 



" Notes on the Atmospheric Lines of the Solar Spectrum and on 

 certain Spectra of Gases." By Dr. John Hall Gladstone, F.R.S. 



In the paper of Sir David Brewster and myself on the lines of the 

 solar spectrum *, attention was drawn to the following among other 

 phenomena : — 



1st. "When the sun descends towards the horizon and shines 

 through a rapidly increasing depth of air, certain lines which before 

 were little if at all visible, became black and well defined, and dark 

 bands appear even in what were formerly the most luminous parts of 

 spectrum." These we termed "atmospheric lines." We did not 

 wish to express by that term anything beyond the fact above men- 

 tioned ; yet we threw out the idea that these lines may have their 

 origin "in the air that encircles our globe." 



2nd. In the case of those artificial flames whose spectra " consist of a 

 series of luminous bands separated by dark spaces . . . these luminous 

 bands sometimes coincide with the dark lines of the solar spectrum." 



About the same time KirchhofFf published his theory that this 

 remarkable coincidence is due to the presence in the atmosphere of 

 the sun of the substances which emit these luminous bands, and 

 their appearance as dark lines is because "the spectrum of an 

 incandescent gas becomes reversed, when a source of light of suffi- 

 cient intensity, giving a continuous spectrum, is placed behind the 

 luminous gas." It also appears that " sodium vapour at a tempe- 

 rature much below that at which it becomes luminous, exerts its 



* Philosophical Transactions, 1.860, p. 149. 

 f Pogg. Ann. cix. pp. 148, 275 ; ex. p. 187. 



