With respect to Unity of Purpose, it is sufficient to observe, that,
where the attention is at the same time claimed by two objects, having
each a different end, they must of necessity break in upon that free
state required of the mind in order to receive a full impression from
either. It is needless to add, that such conflicting claims cannot,
under any circumstances, be rendered agreeable. And yet this most
obvious requirement of the mind has sometimes been violated by great
Artists,--though not of authority in this particular, as we shall
endeavour to show in another place.

We proceed, meanwhile, to the second principle, namely, Variety; by
which is to be understood _difference_, yet with _relation_
to a _common end_.

Of a ruling Principle, or Law, we can only get a notion by observing the
effects of certain things in relation to the mind; the uniformity of
which leads us to infer something which is unchangeable and permanent.
It is in this way that, either directly or indirectly, we learn the
existence of certain laws that invariably control us. Thus, indirectly,
from our disgust at monotony, we infer the necessity of variety. But
variety, when carried to excess, results in weariness. Some limitation,
therefore, seems no less needed. It is, however, obvious, that all
attempts to fix the limit to Variety, that shall apply as a universal
rule, must be nugatory, inasmuch as the _degree_ must depend on the
_kind_, and the kind on the subject treated. For instance, if the
subject be of a gay and light character, and the emotions intended to be
excited of a similar nature, the variety may be carried to a far greater
extent than in one of a graver character. In the celebrated Marriage at
Cana, by Paul Veronese, we see it carried, perhaps, to its utmost