Thomas Edison may not be everyone's favorite inventor, but it's hard to argue that he wasn't always working, trying to figure out what the next engineering innovations would be. These excerpts from a 1888 to-do list offer some insight into Edison's ideas for the next big thing.
Edison was a prolific note-taker and list-maker, filling notebooks upon notebooks with his thoughts and ideas. The Thomas Edison Papers is currently in the process of digitizing Edison's writings, among them this 1888 list, "Things doing and things to be done." From lists like this, it's easy to see how Edison ended up holding more than 1,000 patents; he was constantly making lists of possible products and innovations. Some items from this particular list (transcribed by Brain Pickings):
New standard phonograph
Hand turning phonograph
New expansion pyromagnetic dynamo
Ink for blind
Top image from Wikimedia Commons.