Royal Society articles can now be downloaded for free
The Notes and Records is a periodical publication by the Royal Society and is now available for free download. Many published articles relate to microscopy.
Magazine articles on microscopy
Popular Science magazine published many different articles dealing with microscopy. These articles can be accessed over Google Books:
Here is yet another link to an article from Popular Science magazine.
Stains and reagents for microscopy
I found an article in Popular Science Magazine (see link below) which gives a general overview of different stains that can be used in microscopy.