An early telephone schematic found in a very special category on Wikimedia Commons.
Wikipedia Commons user "Minutemen" took this polarization-microscope image of liquid crystal.
Click to embiggen vastly Is it smiling at you? From Louisa Howard at the Dartmouth Electron Microscope Facility.
Simon Andrews took this microscopic photograph of a cell cluster of coelastrum algae and submitted it to Wikimedia Commons, where I found it.
From The New Students Reference Work (1914), edited by Chandler B. Beach, associate editor Frank Morton McMurry. Scanned by Wikimedia Commons user LA2.
Astronomical charts from Gujin Tushu Jicheng, a Qing dynasty Chinese encyclopedia.