these, others have added virtue, knowledge, discretion, equality in age
and fortune, and, as _Cicero_ calls it, _morum comitas_, a pleasantness
of temper.

18. If I were to give my opinion upon such an exhausted subject, I
should join to these other qualifications a certain æquibility or
evenness of behaviour. A man often contracts a friendship with one whom
perhaps he does not find out till after a year's conversation: when, on
a sudden, some latent ill-humour breaks out upon him, which he never
discovered or suspected at his first entering into an intimacy with him.

19. There are several persons who, in some certain periods of their
lives, are inexpressibly agreeable, and in others as odious and
detestable. _Martial_ has given us a very pretty picture of one of these
species in the following epigram:

_Difficilis facilas, jocundus, acerbus, es idem_,
_Nec tecum possum vivere; nec sine te_. Epig. 47. 1. 12.

In all thy humours, whether grave or mellow,
Thou'rt such a touchy, testy, pleasant fellow;
Hast so much wit and mirth, and spleen about thee,
There is no living with thee nor without thee.

20. It is very unlucky for a man to be entangled in a friendship with
one, who by these changes and vicissitudes of humour is sometimes
amiable, and sometimes odious: and as most men are at some times in an
admirable frame and disposition of mind, it should be one of the
greatest tasks of wisdom to keep ourselves well when we are so, and
never to go out of that which is the agreeable part of our character.