Refraction of the Elements and their Chemical Equivalents. 143 

 Univalent Metals. 



This confirms the conclusions drawn in 1877, the mean product for 

 the univalent metals, omitting sodium, being T30. This is in spite 

 of the fact that lithium and caesium differ from one another in either 

 factor in the ratio of about 9 to 2. The two metals below the line, 

 though acting as monads in the compounds from which these values 

 are deduced, are considered to be dyad and triad respectively. With 

 them, the product is a little higher ; this will be referred to after- 

 wards. 



Bivalent Metals. 



With the exception of beryllium, those metals which are properly 

 bivalent agree closely, although giving values distinctly below that 

 of the former list. The mean of the values is 0'99. The remaining 

 five metals, which have well-marked higher valencies, have, as in the 

 case of the corresponding univalent elements, a somewhat higher 

 value. 



VOL. LX. M 



