On Transmission of Light through an Atmosphere. old 



where the deposits in the Bay of Bengal are probably the 

 cause of its great depth; and where earthquakes in the 

 intervening regions betray when the faults are establishing 

 themselves which render the rising and the descending areas 

 independent of one another, and allow the denudation on the 

 one side and the deposition on the other to produce each its 

 full effect, without mutual interference. 



Of course all compressions and dilatations must be accom- 

 panied by other movements Avithin the earth, and at all 

 depths ; which may be slow but are no less sure. In fact, 

 there is no material which can resist yielding to differences 

 of pressure, however feeble, if they act for a long time and 

 over a large surface ; and such pressures, urging in various 

 directions, must arise both from the compressions and dilata- 

 tions spoken of above, and from other causes, among which 

 movements of heat and the heterogeneous character of the 

 materials of which the earth consists are prominent. The 

 earth, therefore, is in a state of never-ending change, which 

 to become conspicuous to man would only need to be placed 

 in some kind of kinematograph arrangement which would 

 hurry over millions of years in fractions of a second. These 

 effects mix with and complicate those which have been taken 

 account of in the present paper. 



It is interesting to note how the agencies we have been 

 considering would operate upon other bodies of the universe. 

 Events equivalent to denudation and deposition which cause 

 excessively slow movements in our small earth, would act w T ith 

 increased promptness upon such great planets as Jupiter, 

 Saturn, Uranus, and Neptune, and with violence upon bodies 

 that attain the size of the sun and stars. On the other 

 hand, on bodies with the dimensions of the moon they are 

 relatively feeble, and must be very slow in producing any 

 appreciable effect. 



XXXIV. On the Transmission of Light through an Atmosphere 

 containing Small Particles in Suspension, and on the Origin 

 of the Blue of the Sky. By Lord Rayleigh, F.R.S* 



rpHIS subject has been treated in papers published many 

 J- years ago |. I resume it in order to examine more 

 closely than hitherto the attenuation undergone by the 

 primary light on its passage through a medium containing 

 small particles, as dependent upon the number and size of the 

 particles. Closely connected with this is the interesting 



* Communicated by the Author. 



t Phil. Mag. xli. pp. 107, 274, 447 (1871) ; xii. p. 81 (1881). 



