额外的75秒来自哪里？

Question

在朱利安日计算器上编写一些单元测试时,我发现1847年12月2日之前的日期被NSDate错误地初始化.他们似乎有75秒加入.我找不到任何指向那个日期的东西(这是在格里高利历年截止之后).这是一个错误还是我没有遇到历史性的日历调整？

int main(int argc, const char * argv[])
{
    @autoreleasepool {

        NSCalendar *cal = [NSCalendar currentCalendar];
        NSDateComponents *dateComps = [NSDateComponents new];
        dateComps.year = 1847;
        dateComps.month = 12;
        dateComps.day    = 1;
        NSDate *d1 = [cal dateFromComponents:dateComps];
        NSLog(@"d1 = %@", d1);

        dateComps = [NSDateComponents new];
        dateComps.year = 1847;
        dateComps.month = 12;
        dateComps.day    = 2;
        NSDate *d2 = [cal dateFromComponents:dateComps];
        NSLog(@"d2 = %@", d2);
    }
    return 0;
}

输出:

d1 = 1847-12-01 00:01:15 +0000

d2 = 1847-12-02 00:00:00 +0000

Answer 1

根据http://www.timeanddate.com/worldclock/clockchange.html?n=136&year=1847,当时有75秒的时间向前移动.

在伦敦,当地时间将于1847年12月1日星期三凌晨12点00分到达时钟,时钟推进到1847年12月1日星期三12:01:15 AM.

Answer 2

在回答Richard Krajunus的帖子时,以下是大多数计算机用来跟踪这些变化的zoneinfo数据库的一些附加信息:

# From Paul Eggert (1993-11-18):
#
# Howse writes that Britain was the first country to use standard time.
# The railways cared most about the inconsistencies of local mean time,
# and it was they who forced a uniform time on the country.
# The original idea was credited to Dr. William Hyde Wollaston (1766-1828)
# and was popularized by Abraham Follett Osler (1808-1903).
# The first railway to adopt London time was the Great Western Railway
# in November 1840; other railways followed suit, and by 1847 most
# (though not all) railways used London time.  On 1847-09-22 the
# Railway Clearing House, an industry standards body, recommended that GMT be
# adopted at all stations as soon as the General Post Office permitted it.
# The transition occurred on 12-01 for the L&NW, the Caledonian,
# and presumably other railways; the January 1848 Bradshaw's lists many
# railways as using GMT.  By 1855 the vast majority of public
# clocks in Britain were set to GMT (though some, like the great clock
# on Tom Tower at Christ Church, Oxford, were fitted with two minute hands,
# one for local time and one for GMT).  The last major holdout was the legal
# system, which stubbornly stuck to local time for many years, leading
# to oddities like polls opening at 08:13 and closing at 16:13.
# The legal system finally switched to GMT when the Statutes (Definition
# of Time) Act took effect; it received the Royal Assent on 1880-08-02.
#
# In the tables below, we condense this complicated story into a single
# transition date for London, namely 1847-12-01.  We don't know as much
# about Dublin, so we use 1880-08-02, the legal transition time.

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