On 2018-03-19 22:51, Paul Eggert wrote abput my proposal to change the switches on 1883-11-18 in the US to a single instant:
But we have a reliable eyewitness account that New York had two noons that day. See the quotation from William F. Allen in the "northamerica" file, taken from Bartky's 1989 paper <http://dx.doi.org/10.2307/3105430>. So the New York switch cannot have been at 18:00 GMT that day, as that would have meant two instances of 13:00, not two instances of 12:00. Bartky writes that it was called the "day of two noons" because eastern parts of the new zones observed noon twice, which wouldn't have happened if everyone switched at 18:00 GMT.
Allen also wrote that New York got its time signal from the Naval Observatory, not from the Allegheny Observatory. Back then, different observatories were competing for the time-setting business. Perhaps the SpaceWatchtower sources included Allegheny partisans? (It's hard to tell from its source list.)
It's possible that parts of the US switched at around 12:00 local time while other parts switched at 18:00 GMT; but if that's the case, I'd like sources for which parts switched which way.
Yes, I do not know a primary source supporting my propsal, so you are right to ignore it. On the other hand, one cannot trust [Bartky 1989] in this technical matter: he implies on [page 49] that the railway time scales switching on 1883-11-18 started the new scale with 1883-11-18 + 12 h while he reproduces a primary source on [p 50] that shows that the new scale in Louisville, KY started with 1883-11-18 + 10 h, so that no "double noon" could occur. Michael Deckers.