About 17th century books.

The ink is blue now, but it wasn't necessarily blue then...

Kitti said:

There used to be a rhyme and reason, at least through the sixteenth century, though it seems to start falling apart in the late seventeenth century. The long s was originally used in almost all cases. The short s was to be used only 1) at the end of a word 2) as the second s in a double-s construction (i.e. hisses = hifses)

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John Donne made full use of the potential of the long 's'.

cethklein said:

Someone at some point apparently felt the need to write in the book. A few people, apparently. but notice one of the things is written in blue ink. I wasn't aware blue ink was used in the late 19th century. Am I incorrect?

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It was certainly used in the late 19th century--I have several diaries from the 1880s that are written in blue ink. But it was also available before then. Do a search of Google Books for "blue ink" in books published before the 1860s and you'll find recipes for making it dating at least as far back as 1735. And a gem of a poem by Rose Ellen H--, in a book published 1845. It begins:

TO A GENTLEMAN WHO QUIZZED ME FOR WRITING WITH BLUE INK.
Go quiz my ink, but do not frown
On a colour of such renown ;
For I believe the pleasing hue,
Some persons think, types love's pow'r true :
I really hardly know this well,
But still I find I love blue well.

It appears that the same types of people who used blue ink in past centuries are the same as those who type in pink on modern day message forums. That poem could've been written yesterday. I've seen people defend themselves using the same words.

I love that poem.

Kitti's right.