[tz] Irish time...

Joseph S. Myers jsm at polyomino.org.uk
Sun Oct 16 13:43:57 UTC 2011

On Sun, 16 Oct 2011, Kevin Lyda wrote:

> The first entry in the europe zone file for Ireland is as follows:
> Rule    GB-Eire 1916    only    -       May     21      2:00s   1:00    BST
> However I don't think it's correct.  I'm not sure how far back we want
> to go, but apparently from 1880 up until October, 1916, Dublin was 25
> minutes off from London.  When the clocks were set back in October
> 1916, they were set back 35 minutes - which would seem to cast doubt
> on the second line for GB-Eire:
> Rule    GB-Eire 1916    only    -       Oct      1      2:00s   0       GMT

The effect as shown by zdump appears to be correct:

Europe/Dublin  Sun May 21 02:25:20 1916 UTC = Sun May 21 01:59:59 1916 DMT isdst=0 gmtoff=-1521
Europe/Dublin  Sun May 21 02:25:21 1916 UTC = Sun May 21 03:00:00 1916 IST isdst=1 gmtoff=2079
Europe/Dublin  Sun Oct  1 02:25:20 1916 UTC = Sun Oct  1 02:59:59 1916 IST isdst=1 gmtoff=2079
Europe/Dublin  Sun Oct  1 02:25:21 1916 UTC = Sun Oct  1 02:25:21 1916 GMT isdst=0 gmtoff=0

That is, the clocks went forward one hour at 2am DMT on 21 May, and then 
at 2am DMT (3am summer time) on 1 October they went to GMT.  See attached 
scans of the relevant laws.

The relevant UK National Archives file has a public information poster 
used in Ireland to inform people of the 35-minute clock adjustment.  What 
times people were actually using in Ireland, I don't know.

I have not attempted a thorough survey of Irish laws relating to time; my 
2005-01-26 comment in the europe file lists those I found (though those 
URLs seem to have become broken since then) but I haven't attempted to 
match them up to individual transitions and add comments for each 
transition giving the Irish legal basis for it alongside those giving the 
British basis.

Joseph S. Myers
jsm at polyomino.org.uk
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