THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



APRIL 1863. 



XXXIV. On Celestial Dynamics. By Dr. J. R. Mayer*. 



I. Introduction. 



EVERY incandescent and luminous body diminishes in tem- 

 perature and luminosity in the same degree as it radiates 

 light and heat, and at last, provided its loss be not repaired from 

 some other source of these agencies, becomes cold and non- 

 luminous. 



For light, like sound, consists of vibrations which are com- 

 municated by the luminous or sounding body to a surrounding 

 medium. It is perfectly clear that a body can only excite such 

 vibrations in another substance when its own particles undergo 

 a similar movement ; for there is no cause for undulatory motion 

 when a body is in a state of rest, or in a state of equilibrium 

 with the medium by which it is surrounded. If a bell or a 

 string is to be sounded, an external force must be applied ; and 

 this is the cause of the sound. 



If the vibratory motion of a string could take place without 

 any resistance, it would vibrate for all time ; but in this case no 

 sound could be produced, because sound is essentially the pro- 

 pagation of motion ; and in the same degree as the string commu- 

 nicates its vibrations to the surrounding and resisting medium 

 its own motion becomes weaker and weaker, until it at last sinks 

 into a state of rest. 



The sun has often and appropriately been compared to an in- 

 cessantly sounding bell. But by what means is the power of 



* Beitrage zur Dynamik des Himmeh, in popularer Darstellung, von Dr. 

 J. R. Mayer, Stadtarzt in Heilbronn. Heilbronn, 1848. Translated bv Dr. 

 H. Debus, F.R.S. 



Phil. Mag. S. 4. Vol. 25. No. 168. April 1863. R 



