On April 11th, the pair went in Reynolds's coach to dine with Cambridge,
at Twickenham. Johnson was in high spirits. He remarked as they drove
down, upon the rarity of good humour in life. One friend mentioned by
Boswell was, he said, _acid_, and another _muddy_. At last, stretching
himself and turning with complacency, he observed, "I look upon myself
as a good-humoured fellow"--a bit of self-esteem against which Boswell
protested. Johnson, he admitted, was good-natured; but was too irascible
and impatient to be good-humoured. On reaching Cambridge's house,
Johnson ran to look at the books. "Mr. Johnson," said Cambridge
politely, "I am going with your pardon to accuse myself, for I have the
same custom which I perceive you have. But it seems odd that one should
have such a desire to look at the backs of books." "Sir," replied
Johnson, wheeling about at the words, "the reason is very plain.
Knowledge is of two kinds. We know a subject ourselves, or we know where
we can find information upon it. When we inquire into any subject, the
first thing we have to do is to know what books have treated of it. This
leads us to look at catalogues, and the backs of books in libraries."

A pleasant talk followed. Johnson denied the value attributed to
historical reading, on the ground that we know very little except a few
facts and dates. All the colouring, he said, was conjectural. Boswell
chuckles over the reflection that Gibbon, who was present, did not take
up the cudgels for his favourite study, though the first-fruits of his
labours were to appear in the following year. "Probably he did not like
to trust himself with Johnson."

The conversation presently turned upon the _Beggar's Opera_, and Johnson
sensibly refused to believe that any man had been made a rogue by seeing
it. Yet the moralist felt bound to utter some condemnation of such a