Useful links when researching vintage patents
European Patent Office — https://worldwide.espacenet.com
My goto resource for vintage patents. Great search facilities and worldwide coverage.
Google Patents — https://patents.google.com
Google's search engine for patents. Quite good, but I prefer the EPO's user interface. Quite often Google links to the EPO website for details.
U.S. Patent Office — https://www.uspto.gov
This site also has trademark information, but the user interface is often confusing and it only covers U.S. documents.
The Lens Patent Search — https://www.lens.org/lens/search/patent/structured
A good resource when searching by inventor names.
PatBase — http://www.patbase.com
A commercial patent database, but they have a free “patent classification explorer”.
Useful links when researching historical information
FamilySearch — https://familysearch.org
A very good website run by the Mormon Church. First port of call for births, marriages, immigration, census information and deaths.
Some of the information is not accessible from the internet, but only from affiliated libraries. My local UK library is one of them. You can find documents using the computers at the library and email them to yourself.
Find A Grave — https://www.findagrave.com/
Good for deaths, but only good for deaths.
FreeCen — https://www.freecen.org.uk/
UK census information up to 1891.
New York Times archive
I can no longer recommend the New York Times archive as a source.
It's a paid subscription that is almost impossible to cancel.
The venerable New York Times has turned into a scam.
Newspapers.com — https://www.newspapers.com/
Paid subscription, but can be cancelled anytime without problems.