Definition of "unmistakable"

Now, I still think that for this box of matches to have escaped the wear of time for immemorial years was a strange, and for me, a most fortunate thing. Yet oddly enough I found here a far more unlikely substance, and that was camphor. I found it in a sealed jar, that, by chance, I supposed had been really hermetically sealed. I fancied at first the stuff was paraffin wax, and smashed the jar accordingly. But the odor of camphor was unmistakable.

1895 May 7, H[erbert] G[eorge] Wells, chapter X, in The Time Machine: An Invention, New York, N.Y.: Henry Holt and Company

Whenever the locomotive was working hard there was unmistakable evidence of its higher power than its predecessors in the brilliant and explosive arcing between conductor shoes and the third rail; this was particularly vivid in Quarry Tunnel in the down direction, where the display equalled anything we have seen on the frostiest of nights in an electrified third-rail area.

1959 March, “The 2,500 h.p. electric locomotives for the Kent Coast electrification”, in Trains Illustrated, page 125