28 Messrs. A. C. and A. E. Jessnp on the 
manganese has no direct evolution products, that is to say, 
there are no elements of higher atomic weight than man- 
ganese with properties sufficiently closely related to manganese 
to justify our considering them as direct evolution products 
of this element. We have therefore placed manganese at the 
head of its own column, and would point out that the blank 
spaces below this element do not necessarily mean that there 
is room for elements to be discovered to fill these, for, as 
will be presently shown (page 36), it is in the highest degree 
improbable that manganese should be able to gi\ e rise to any 
direct derivatives at all. 
Following molybdenum, we have now the three elements 
ruthenium, rhodium, palladium, which clearly may be placed 
under iron, nickel, cobalt. After these three come in ascending 
order twelve elements, silver to cerium, which fall naturally 
into consecutive families as shown in our table. Between 
cerium and tantalum we have all the rare earths, and indeed, 
so little is known of their chemical properties that it is 
impossible to assign any of these to its particular family with 
any degree of confidence. We have, however, ventured to 
assign positions to those rare earths which seem to be known 
definitely, and have followed Emerson Reynolds' example in 
considering praseodymium, neodymium, and samarium as 
belonging to the iron group. We are convinced that the 
rare earths are very abnormal : they are all characterized 
by being trivalent, and this fact alone, which means that the 
external atomic structure is that of a trivalent element, is 
sufficient to differentiate these from the other normally 
developed elements, for in most cases they cannot be evolved 
simply from trivalent antecedents. However, in the section 
of this paper which deals with the question of radioactivity, 
we put forward a suggestion which may account for their 
extraordinary characteristics. The remaining elements after 
tantalum up to uranium may, without question, be assigned 
to the positions shown in our table. 
We may now turn our attention to the four protons, that 
is to say, the four earliest forms of matter existing in nebula?, 
viz., those with wave-lengths 4862, 4959, 5007, and 5876 t.m., 
and endeavour to trace how T the process of evolution from 
these gave rise to the eight elements lithium, beryllium, 
boron, carbon, nitrogen, oxygen, fluorine, and neon. We feel 
that we are justified, in dealing with processes of evolution, 
in saying that the most natural tendency will be for the 
process to take place along a direct line of development. It 
is reasonable to assume that the probable effort of any element 
will be to give rise to an element of its own type. We would 
