Now for the real treat

Most designers know that 12 point was known as a pica, and they could all show off by giving measurements in picas, or pica ems. An em was so called because the letter M nearly always sat on a piece of type metal whose set (width) was the same as its size, giving a nearly square cross section. An en is half an em. Here again this was because the letter n usually sat on a piece of type whose set was half its size. Moreover, the average width of all lower case characters was an en. A w is wider than an n, but a , or i or l are all narrower.
     People of the predigital generation tended to learn things in picas. But post-digital it is still true that a line in a book shouldn't run to more than about 27 picas (four and a half inches) because if you have more than about 54 ens, or characters, to a line the eye tends to have difficulty finding the next line.

Shall we make a detour around lower case? A fount of type used to live in two trays. These two trays, known as type cases, were divided into little sections, each section housing a number of characters in that size. The e compartment held the most letters, because that is the most used letter.
     These trays or drawers lived in a chest of drawers which came to about chest level. On top was a metal stand which held two of these cases, the top one above and slightly beyond the bottom one, allowing a compositor to pick from, or return type to, any section in either case. The bottom tray, or lower case, held the most used characters. The top one, or upper case, held the capitals and other less used characters.
     There are various buffoons nowadays, even in schools like Reading, who are trying to call lower case letters 'small letters'.
     Forget it. It leads to confusion with small caps, and it also leads to confusion over size. Small letters are 6 point. Large letters are 72 point. Small caps X and O, by the way, are usually made to the same height as the lower case x and o. The letters in small caps are proportionately wider than capitals, and proportionally meatier in the stems. Reducing caps to do this job gives a weedy and unpleasant result, which we hope gradually to eliminate in desk-top publishing.
     The upper case held fewer characters, because fewer characters were needed, but as the characters were bigger they tended to need the space anyway. And a font was cast according to the frequency of letters in normal use. Its size was measured by the number of cap A's in the fount. A small fount had three As only. Almost a tenth of the fount should have been an e. But to follow the frequency rule slavishly would have left far too many characters with too few pieces to cover all contingencies.
     But here comes the stuff really worth remembering. Points only came late in the history of printing. Before then the vocabulary developed as vocabulary normally does before some efficiency idiot interferes. Carpenters talk about a 'a fat sixteenth', not 'one point six millimetres'.
     Printers called sizes as follows, and you will see that the sizes were not progressive arithmetically. They were derived from the needs of the typesetter and reader, rather than to fit into any pre-conceived pattern. A pica was not always the exact 12 points we now say it is.

MINIKIN           3pt
BRILLIANT         3.5pt
GEM               4pt
DIAMOND           4.5pt
PEARL             5pt
RUBY or AGATE     5.5pt 
NONPAREIL         6pt    
                       pronounced 'nonparrel'  
MINION            7.3pt  
                       does Adobe know?  
BREVIER           7.6pt  
                       pronounced 'brev-ear'  
BOURGEOIS         8.5pt  
                       pronounced 'ber-joyce'  
LONG PRIMER       9.5pt  
                       pronounced 'longprimm-er'  
SMALL PICA       10.5pt  
                       pronounced 'pie-ker'  
PICA             12.2pt	
ENGLISH          12.5pt
2-LINE BREVIER   about 15pt
GREAT PRIMER     about 17pt
PARAGON          about 19pt
DOUBLE PICA      about 21pt
2-LINE PICA      about 24.4pt
2-LINE ENGLISH   about 25pt

Perhaps we should get Microsoft Word to have various default sizes? Footnotes in brevier, text in small pica and headlines in great primer?
     And at this point the author is as bored with this stuff as you must be. So we end by hoping that you enjoy learning what you will about this business of committing words to any one of a number of media. It is by far the best way of communication that exists.

And it is fun.