<602 



Mr. Olive Cnthbertson on the 



into larger or less stable molecules, the new free frequencies 

 introduced between the atoms of the compound would be 

 slower than those between the atoms of the elements, with a 

 'Correspondingly greater effect on the dispersion. 



It should be noted that, in these cases, the only practicable 

 test of our hypothesis is the converse of that which gives 

 such promising results in the case of the halogens. There 

 we neglected the interatomic ref inactivities of one element 

 and the compound, and obtained a value for the atomic re- 

 fractivity of the other element. Here we neglect the inter- 

 atomic refractivities of both elements and obtain a value for 

 the interatomic refractivity of the compound, and this, being 

 the difference between two nearly equal quantities, is liable 

 to much larger errors than the atomic. 



In this group the most interesting results are obtained in 

 the case of ozone. Here the refractivity is 21^ per cent, 

 higher than the value for three atoms of oxygen, and the 

 dispersive power is much greater. If we deduct from the 

 experimental values for the refractivity of ozone one and a 

 half times the refractivity of oxygen, we obtain the following 

 result: — 



\ x 10 8 . 



[„-l] 03 XlO* ... 



C708 



5461 



4800 



50764 



52000 



53290 



3r -.1 



a0-i] 02 xio«. 



40428 



40755 



41049 



Difference X 10 s .. 



10336 



11245 



12241 



The figures in the last line, which represent the increase 

 in refractivity due to the interatomic effect in ozone, are 

 fitted by the curve given by 



r 11v1A8 -12660 x 10 27 



The wave-length which corresponds with « 2 = 1424*8 x ] 27 

 is X = 2520. The absorption spectrum of ozone has been 

 most recently measured by Meyer (Drude's Ann. xii. p. 849 

 (1903)), who found a maximum of absorption at A, 2580. 



One other fact with regard to this substance is worth 

 mention. If we calculate the constants of the expression 

 for the refractivity of ozone from the values given in the 

 first line above for X6708 and X4800, we obtain a curve 



