Mantle clocks are mantel clocks.  Did I just say that?  Or did you just wonder what you read?  The two spellings of the same word, mantle and mantel, are used almost interchangeably nowadays.  As I write this blog post, I am looking up how many times mantle clocks and mantel clocks each show up?  Honest, I haven’t looked before, but let’s find out together.

OK.  Done.  Mantle clocks yields about 739,000 results in a Google search.  And mantel clocks?  Only 278,000 Google search results.  I am really shocked, I must say!  I have always thought mantel clocks was the “American” spelling and mantle clocks was the European spelling.  Apparently but not necessarily so.

Let’s move on to the dictionary definitions of mantle clocks and mantel clocks, and see if we glean any horological spelling insights, or clock terminology country of origin insights.  I will now check the Random House dictionary online.  I left my horological dictionary at home — just kidding, don’t have such a clocks dictionary …. not sure if I’ve ever even seen one before, and I’ve seen more clocks books of all types than I care to mention.  Anyhow, on to the dictionary definitions of mantle clocks and mantel clocks.  Ladies and Gentleman, place your clocks bets!

Well this is interesting and not very conclusive.  Looking at the origins of the 2 terms:

mantel

1489, “short, loose, sleeveless cloak,” variant of mantle (q.v.). Sense of “movable shelter for soldiers besieging a fort” is from 1524. Meaning “timber or stone supporting masonry above a fireplace” first recorded 1519, a shortened form of M.E. mantiltre “mantletree” (1482). Mantelpiece is from 1686.
mantle

O.E. mentel “loose, sleeveless cloak,” from L. mantellum “cloak,” perhaps from a Celtic source. Reinforced and altered 12c. by O.Fr. mantel (Fr. manteau ), from the L. source. Allusive use for “symbol of literary authority or artistic pre-eminence” is from Elijah’s mantle [2 Kings ii.13]. As a layer of the earth between the crust and core (though not originally distinguished from the core) it is attested from 1940. The verb meaning “to wrap as in a mantle” is attested from mid-15c.
Online Etymology Dictionary, © 2010 Douglas Harper
In appears Mantle has been in use since the 12th century, and Mantel has been in use since the 14th century, with similar meanings throughout time and many centuries.
Whom are we to argue — we will continue to use both spellings, mantle clocks and mantel clocks.  And don’t forget, the clocks can go either on your mantel or mantle.