15 Feb
2008
15 Feb
'08
3:05 p.m.
Relays: Possible, but even in 1945 was very hard.
Available by 1901 at
the latest.
I would say relays were definitely available in 1900. I have a book from
1895 [1] on electric bells, and while I can't remember if relays are
explicitly mentioned (I think they are), the trembler bell was certainly
well-known at that time.
A trivial modification to a trembler bell turns it into a relay with one
normally-closed contact (just remove the hammer and gong, and electrically
disconnect the contact from the coil and bring them out seprately). It's
then only a very small step to add a normally-open contact, and indeed
other cotnacts.
[1] My second-oldest book on electrical stuff. I have an 1892 book on
telephone installations.
-tony