OF ARTS AND SCIENCES. 



413 



In this Table, the seventli column gives the values of the interferential 

 constant I. The eighth is obtained by multiplying the numbers in 

 column six. by the molecular weights of the corresponding substances, 

 divided by 100, so as to avoid many figures. The product 31 1 gives, 

 tlierefore, the number of interference bands between G and G for a 

 tliickness of each liquid proportioned to its molecular weight. 



I have employed the measurements of Landolt and. Haagen in dis- 

 cussing the question whether the interferential constant of a definite 

 chemical compound is the sum of the interferential constants of its 

 constituent atoms. Table V. exhibits the methods and results of this 



discussion. 



TABLE V. 



