Like most of today's single-volume dictionaries, Johnson's work was encyclopedic: when he wanted to define prism he went straight to the horse's mouth and quoted directly from Isaac Newton.
But it was American successors to Johnson who carried on the encyclopedic tradition, including names of people and places as standard in their A-Z word lists. In the 1980s British dictionaries began to adopt this approach; they also borrowed the American convention of giving compound words such as lawn tennis the same status as single words, rather than burying them under their first element (in this case lawn).
American lexicographers took the "describe, don't prescribe" philosophy to heart, sometimes with controversial results. When Webster's Third New International Dictionary, Unabridged was published in 1961 it caused a furore with (among other things) its scrupulously neutral description of the word ain't: "though disapproved of by many and more common in less educated speech, (it is) used orally in most parts of the US by many cultivated speakers, esp. in the phrase ain't I."
Rather than being praised for its objectivity, Webster's Third was lambasted in the press. The Toronto Mail and Globe thundered that the dictionary's "embrace of the word ain't will comfort the ignorant, confer approval upon the mediocre, and subtly imply that proper English is the tool of only the snob". This reaction - difficult to imagine in Britain - tells us a great deal about the status of the dictionary in melting-pot America, where its role as an arbiter of correct usage is seen as more important than in the UK.