We have measured the combination of hydrogen Lamb shifts L(1S) - 5L(2S
) + 4L(4P) by comparing the frequencies of the 1S-2S and 2S-4P transit
ions. The measurement determines the 1S Lamb shift to be 8 172 827(51)
kHz, the most precise value for any Lamb shift. The theoretical predi
ctions for L(1S) are 8 172 802(30) and 8 172 654(40) kHz, correspondin
g to proton charge radius values of 0.862(12) and 0.805(11) fm, respec
tively.