From wikipedia on Morse code:

> In his earliest code, Morse had planned to transmit only numerals, and to use a codebook to look up each word according to the number which had been sent. However, the code was soon expanded by Alfred Vail in 1840 to include letters and special characters, so it could be used more generally. Vail estimated the frequency of use of letters in the English language by counting the movable type he found in the type-cases of a local newspaper in Morristown. //

M [1] is always well down the frequency in general lists. I wonder if Vail's corpus was biased, whether he discounted local names.

Interesting to note that Morse planned a code using a dictionary; should we be calling it Vail code?

[1] http://letterfrequency.org/