( 606 ) 



1,8 X 10-'" sec, 

 i. e. in a time equal to 18000 times the value we have found for t. 

 We see in this way that it cannot be the encounters between mole- 

 cules, by wliich the regular succession of \ibrations comes to an end. 

 It seems to be disturbed much more rapidly by some other cause 

 which is at work within each molecule. 



In the case of the sodium flame there is a similar difference 

 between the length of time r and the mean interval between two 

 encounters. 



^ 15. Wc shall now return for a moment to the resistance that 

 has been spoken of in § 5, tlie only one that is really exerted by 

 the aether. This resistance is intimately connected with the radiation 

 issuing from a vibrating electron, and if a beam of ligiit were 

 weakened by its influence, this would be due to part of the incident 

 energy being withdrawn from the beam and emitted again into the 

 aether. C)f course, this could hardly be called an absorption. But, 

 apart from this objection, we can easily show that the resistance in 

 question is much too small to account for the diminution of intensity 

 that is really observed. Its component in the direction of .v is 



e' (i'x 

 6 jrc' Tt' ' 

 or, for harmonic vibrations of frequency n, 



n' e' d X 



6 jr c' (it 

 Comparing this witli (8), we find 



_ 7i'e' 



6 JT c' 



This amounts to 2,0 X lO^^' for carbonic dioxyd (for the wave- 

 length ;. = 2,60 ft (§ 9)) and to 4,0 X lO-^" in the case of the 

 sodium tiame. These numbers are far below those which result from 

 (18), if we substitute the value that has been calculated for t. We 

 then get, for carbonic dioxyd 4,0X10"'', and for the sodium flame 

 a number between 1,2 X io-ie and 0,6 X 10-'«. 



^ 16. It has already been shown in § 8 that an increase of ij 

 broadens the absorption band, diminishing at the same time the ab- 

 sorption in its middle. Indeed, in many cases we may say that 

 the broader the band, the feebler is the absorption for a definite 

 kind of rays. 



The question now arises what is the total amount of energy 



