ELISHA MITCHELL SCIENTIFIC SOCIETY 19 
made if some hypothesis as to the cause of this variability 
were proposed. This difference between the two attitudes has 
seldom been properly realized. While some chemists, accept- 
ing the constant valency of atoms, have attempted to deduce 
the varying atomic linking frem one distinct point of view, 
others have considered it sufficient to have assigned to the 
atom of a particular element in one compound one valency, 
and in another compound a different valency, according as 
this or that value appeared the most suitable, and thus to 
have given a so-called explanation of the composition of the 
compounds in question. In this way the fact has been over- 
looked, that an arbitrary interpretation carried out by means 
of chosen hypotheses, cannot be regarded as an attempt ata 
scientific explanation, but is nothing more than an expression 
of our ignorance of the causal connection of the phenomena 
An explanation would require that the different valencies as- 
signed to one and the same element in different compounds, 
should be traced to a different cause. If, for instance, it is 
stated that carbon in carbon dioxide possesses double the val- 
ency which it possesses in carbon monoxide, such a statement 
is no explanation of the fact thae an atom of carbon in the 
former compound is combined with twice as much oxygen as 
in the latter, for such a statement is merely a paraphrase 
which hides its incompetency by assuming the form of an ex- 
planation. Although this may be perceived without further 
remark, still it has frequently occurred during the past few 
years that similar paraphrases have not only been proposed 
but also accepted as real explanations of such phenomena. 
Just as it was formerly supposed that the assumption of a vi- 
tal force dispensed with a complete investigation of the phe- 
nomena of animal life, somany chemists have of late thought 
that they possessed in ‘ variable valency,’ a means of explain- 
ing the varying stoichiometric relationships which would sat- 
isfy all claims. Such deceptions can only retard the advance 
of the science, since they prevent an earnest and thorough in- 
vestigation of the question, whether each atom is endowed 
with a property determining and limiting the number of atoms 
with which it can combine, dependent upon the intrinsic na- 
