While Musical Math is under production (in between many other projects), here's an excerpt from the Form of the Book by Jan Tschichold--part of demo content that comes with the tachyons css framework on which this landing page is based.
TYPOGRAPHY, even when poorly executed, can never be taken for granted; nor is it ever accidental. Indeed, beautifully typeset pages are always the result of long experience. Now and then they even attain the rank of great artistic achievement. But the art of typesetting stands apart from expressive artwork, because the appeal is not limited to a small circle. It is open to everyone's critical judgment, and nowhere does this judgment carry more weight. Typography that cannot be read by everybody is useless. Even for someone who constantly ponders matters of readability and legibility, it is difficult to determine whether something can be read with ease, but the average reader will rebel at once when the type is too small or otherwise irritates the eye; both are signs of a certain illegibility already.
All typography consists of letters. These appear either in the form of a smoothly running sentence or as an assembly of lines, which may even have contrasting shapes. Good typography begins, and this is no minor matter, with the typesetting of a single line of text in a book or a newspaper. Using exactly the same typeface, it is possible to create either a pleasant line, easily read, or an onerous one. Spacing, if it is too wide or too compressed, will spoil almost any typeface.