2 JOURNAL OF THE 
the elements. At several times during the century a wider 
vision has made it necessary to recast the definition of the 
elements to accord with increasing knowledge. It would 
seem as if another such period of change were approaching. 
There may be need of a truer definition, and how shall this 
be realized or the new definition properly fitted unless the 
knowledge gained be summed up and appreciated? 
The conception of an element among the Greek philoso- 
phers and the earlier alchemists was very different from the 
modern idea. ‘This conception sprang from the theories as to 
the formation of the material universe. ‘The elements were 
the primal forms of matter seen only combined, impure, 1m- 
perfect. They were the essences or principles out of which 
all things were evolved. In the four-element theory, which 
was so widely spread among the ancients, the fire, air, earth 
and water were not the ordinary substances known under 
these names, but the pure essences bestowing upon fire and 
water their peculiar properties. These essences were not 
thought of as actual substances capable of aseparate materi- 
al existence, and gradually the belief that a transmutation 
was possible between them sprang up. Thus they themselves 
might be derived from some one of them, as fire or water. 
The Thalesian theory deriving all things from water was es- 
pecially popular and was not completely overthrown until the 
modern era. 
When, later on, the alchemists conceived of all metals as 
composed of sulphur and mercury it was an essence or spirit 
of mercury that was meant. Certain common characteristics 
as luster, malleability, fusibility, combustibility, etc.,natural- 
ly led them to think of the metals as belonging to the 
same order of substances containing the same _ princi- 
ples, the relative proportions and purity of which deter- 
mined the variations in the observed properties. Thus the 
properties of the metals depended upon the purity of the mer- 
cury and sulphur in them, the quantities of them and their 
degree of fixation. The more easily a metal was oxidized on 
being heated, the more sulphur it contained, and this sulphur 
also determined its changeability. The more malleable it 
