Evolution and Devolution of the Elements. 47 
is known, and owing to the many uncertainties which exist in 
the atomic weights of the elements, and the number of them 
which are not yet discovered, it is exceedingly difficult to 
obtain even an approximation to a law for devolution, 
However, there is one group which is fairly complete, viz. 
group II., and if any law is to be derived, it is naturally to 
this group that we should look for information. 
The atomic weights of the members of this family are as 
follows : — 
Proto-bervllium between 1 and 4 
Beryllium 9*1 
Magnesium : 24*3 
Calcium 40-1 
Strontium 87*6 
Barium 137*4 
Proto-radium 169-172? 
Radium 225 
The differences between these weights taken in order, 
omitting proto-beryllium for the present, are : — 
Beryllium to magnesium 15*2 
Magnesium to calcium 15*8 
Calcium to strontium 47*6 
Strontium to barium 49'8 
Barium to proto-radium, about. . . 34 
Proto-radium to radium, about. . . 52 
If we subtract the numbers given by the series, which 
correspond to the above values (namely 16 and 52), from 
these values, we obtain the following numbers: — 
Beryllium to magnesium — 0'8 
Magnesium to calcium —0*2 
Calcium to strontium —4*4 
Strontium to barium — 2'2 
Barium to proto-radium, about. . . — 18 
Proto-radium to radium, about. . . 
It will be observed in the foregoing numbers, that alter- 
nate members — 0'8, —4*4, —18, form a descending series ; 
and if we treat other groups of elements in the same way, 
their alternate numbers also invariably form descending- 
series, but, as before mentioned, the number of members in 
these groups being incomplete, we can only observe the 
above-mentioned fact, and are unable to deduce any 
mathematical formula in their case. 
Returning to the series —0*8, —4*4, —18, it is evident that 
this represents the devolution from the standard series 6, 16, 
52. Let us now consider the remaining terms of the series, 
namely —0*2, —2" 2. and 0. 
