1878.] 



President's Address. 



40 



the number of members of the solar system by Professor Asaph. Hall's 

 discovery of the satellites of Mars ; and more recently, Professor 

 Watson has announced his detection of planetary bodies within the 

 orbit of Mercury, during the Solar Eclipse which was visible in 

 America. 



In 1876 Schmidt recorded an outburst of light in a star in Cygnus, 

 which showed a continuous spectrum containing bright lines similar 

 to those of the remarkable star of 1866. As the star waned the 

 continuous spectrum and bright lines faded, all but one bright line in 

 the green, giving the object the spectroscopic appearance of a small 

 gaseous nebula. 



Great progress has been made during the last five years at Green- 

 wich in the method of determining the motions of the heavenly 

 bodies by the displacement of the lines in their spectra, as first 

 successfully accomplished by Mr. Huggins in 1868. Not only do 

 the results obtained by the stars observed at Greenwich agree 

 with those of Mr. Huggins, as satisfactorily as can be expected 

 in so delicate an investigation, but the motions of seventeen more have 

 been determined ; while the trustworthiness of the method has been 

 shown by the agreement of the values for the rotation of the sun and 

 the motions of Venus, with the known movements of these bodies. 

 Mr. Huggins has also obtained photographs of the spectra of some of 

 the brighter stars, which give well defined lines in the violet and ultra- 

 violet parts of the spectrum. These spectra have already shown 

 alterations in the lines common to them and the sun, which are of 

 much interest. 



In Solar Physics, which afford remarkable evidence of Mr. Lockyer's 

 energetic labours in this country and Mr. -Tanssen's in France, I must 

 mention our Foreign Member's wonderful photographs of the sun, 

 wherein the minutest of the constant changes in the granulations 

 exhibited on its surface (and which vary in size from t X q- of a second 

 to 3 or 4 seconds) can be studied in future from hour to hour and day 

 to day; as can also their different behaviour at different periods of 

 the occurrence of sun-spots. 



Before dismissing this fruitful field of research, I must allude to 

 Mr. Lockyer's discovery of carbon in the sun ; and to his announced 

 but not yet published observations on the changes and modifications 

 of spectra under different conditions, some of which he even regards 

 as indicating the breaking up of the atoms of bodies hitherto re- 

 garded as elementary. 



Some important investigations on the Electric Discharge have been 

 communicated to the Society by Messrs. De La Hue and Miiller, and 

 by Mr. Spottiswoode. These, prosecuted by different means, tend to 

 limit the possible causes of the stratification observed in discharges 

 through vacuum tubes. They also point to the conclusion that this 



vol. XXVIII. E 



