11

Logic II 11

burning matter may itself become incandescent, or its heat may
serve to render another more suitable thing incandescent, as
in the Welsbash burner. Here is a complication which will
ordinarily be advantageous, since by not making the same
thing fulfill the two functions of supplying heat to render produce
incandescence of itself incandescing one of incandescing upon being heated, there is more freedom to
choose things suitable to the two functions. This is a good
example of that sort of natural class which Agassiz called
an order; that is, a class created by a useful complication
of a general plan.

Desire always Vague

Closely connected with the fact that every desire is general,
are two other facts very [?] which must be taken into
account in considering purposive classes. The first
of these is that a desire is always more or less variable, or
vague. For example, a man wants an economical lamp.
Then if he burns oil in it, he will endeavor to burn that oil
which gives him sufficient light at the lowest cost. But
another man, who lives a little further from the source of supply