which such materialism carries within its own bosom. In the course of
his reading for his "History of Discoveries relating to Vision, Light,
and Colours," he had come upon the speculations of Boscovich and
Michell, and had been led to admit the sufficiently obvious truth that
our knowledge of matter is a knowledge of its properties; and that of
its substance--if it have a substance--we know nothing. And this led to
the further admission that, so far as we can know, there may be no
difference between the substance of matter and the substance of spirit
("Disquisitions," p. 16). A step farther would have shown Priestley
that his materialism was, essentially, very little different from the
Idealism of his contemporary, the Bishop of Cloyne.

As Priestley's philosophy is mainly a clear statement of the views of
the deeper thinkers of his day, so are his political conceptions based
upon those of Locke. Locke's aphorism that "the end of government is
the good of mankind," is thus expanded by Priestley:--

"It must necessarily be understood, therefore, whether it be
expressed or not, that all people live in society for their mutual
advantage; so that the good and happiness of the members, that is,
of the majority of the members, of any state, is the great standard
by which everything relating to that state must finally be
determined." [15]

The little sentence here interpolated, "that is, of the majority of the
members of any state," appears to be that passage which suggested to
Bentham, according to his own acknowledgment, the famous "greatest
happiness" formula, which by substituting "happiness" for "good," has
converted a noble into an ignoble principle. But I do not call to mind
that there is any utterance in Locke quite so outspoken as the