A fascinating look at the forefront of knowledge in the 17th century - and of course how little was known in many areas. The illustrations are very well drawn, particularly considering the state of development of lenses, microscopy and lighting. In here is the first use of the word "cell" in respect of the building blocks of organisms, and Hooke was probably the first person to see and draw things such as bee stings, nettle leaves, hair, mould... this list is long.
When the book was digitised some of the illustration numbering was cropped, so it can be difficult to identify the appropriate drawing for a particular passage in the text, exacerbated by Hooke or his printer not being particular about where in the text various illustrations were bound. This is harder to negotiate as a pdf of course, because flipping back and forth in clumps of pages is not possible. There's also a handful of pages that seem to have slipped out of the scanner, and only the edges visible. He also uses the 'f' character in place of 's' in many places as was the norm, so it takes a bit of practice and concentration to read at first but well worth the effort.
Notwithstanding the problems, I loved it, and anyone who likes science, the history of science, or just old books will love it too.