One second is the smallest measurement of time on a clock and I am curious to know..?

The word "second" originates from the fact that it is the second division of the hour. Take an hour, divide it into 60 parts once and you have a minute. Divide it into 60 parts a "second" time and you have the second. I guess the "first" youre talking about is the minute... but why is a minute called a minute?

If you really want to get at the etymological roots, it was the mathematicain Ptolemy in Medieval Latin, who first used the term "pars minuta prima" to mean "first small part" in his description of 1/60 of a degree of angle. Our modern "minute" comes from Latin's "minuta" meaning "small", its where we get the adjective minute and the noun minutia. This later became applied to divisions of the hour. The Latin term "secunda minuta" means "second small", shortened to just "second" in English, and refers to the second division of the degree or the hour. This also explains why we use minutes and seconds for both time and angle measure. Why the terms derived for use with angle were ever adopted for time in the first place is not known. Why there are 360 degress about a circle is also open to speculation.

Why 60 and not 100 or 10 or something nice like that? The sexigesimal system (base 60) has its origins in Babylonian, I believe. The numbering system they used still exerts itself in our culture today, as it did in Ptolemy's day, in the way we tell time. There was an attempt to produce a clock that divided the hour into 100... I dont remember when, a century or two ago maybe. It didnt catch on though.

Interestingly, some languages such as Turkish actually have a word for "third", as in the third division of the hour, a sixtieth of a second. Quite unnecessary if you ask me. I dont know when this term came to be but I cant imagine it was before the digital stopwatch.

There was a time in history when there was no second on a clock. This came into being in the late 1600's, well past when the mechanical clock was invented (1300's), and when the clock had enough precision that a smaller unit than a minute became possible. Heck, there was a time when we didnt even have minutes, and all we could do is estimate "half past" or "quarter past" the hour (and that is where we get those terms). Recall that sundials and hour glasses, water clocks and candle sticks were used to tell time.

There is some speculation about where we get the hour, though. It either comes from cultures with base 12 numbering systems, where the day and the night were both separately divided into 12 units each. Or it comes from base 10 systems, where the day and the night were both divided into 10 units each, with two hours reserved for each twilight period. In any case, far enough into history one hour wasnt even the same through the year, because the lengths of the day and the night change over the course of the year, but they were divided into 10 or 12 units anyway, regardless of their length compared to the other half of the day. In fact, if you take a sundial whose face is flat against the Earth, the lengths and divided its face up equally, some hours will pass more quickly than others... thus not even the hours in any given day were equal.

It took better technology than the sundial to standardize the length of the hour. The ancient Greeks standardized the hour, and the hour become 1/24th of the mean solar day.

AM and PM come from these two distinct 12 hour separations of the day. How this got shifted by about six hours to end up with a 12 hour period comprised of both day and night, from midnight to midday, as opposed to the original one period for daylight and the other period for night, is not something I can explain. But you can find discussions on it online.

AM stands for Ante Meridian and PM stands for Post Meridian, both from Latin, meaning before noon and after noon. Meridian is another term for the longitudinal line that passes through your location, so the terms PM and AM describe the suns relation to this line overhead. Ante means before (like the bet you lay *before* seeing your hand), not "anti" which means opposed to or against.

It wasnt but a few centuries ago, before the invention of the railroad, that all times were local, municiple times. Each city had its own time set for the suns passage in the sky. The invention of the railroad made travelling so quick that someone could travel from one city to the next and see a significant difference in local time and their pocket watches. This created a serious problem for railroads, as innaccuracies in train schedules could cause crashes. Thus, the United States originated the time zone concept.

I believe it wasnt until the 1670's or so that the first clocks with a second hand started getting made. It was about this time that the word second entered into English common vocabulary. Ironically though, scientists and the learned at the time had already been speaking of the second as a unit of time for nearly a hundred years before the clock that could track it.

Mechanical clocks were necessary for precise astronomy, science and of course navigation and exploration of the seas. It was always possible to know your latitudinal position by the angle of the North star to the horizon, but figuring out your longitudinal position had been a mystery. Comparing local solar time with the time of a mechanical clock set at a pericular meridian is one was to compute your longitude.

If you take a pendulum clock whose pendulum is 39.1 inches long, the pendulum will swing forward in one second, and back in one second, for a total of two seconds. This is called the "seconds pendulum". Its not necessary to keep track of seconds, but its cool. In fact, the length of such a pendulum was the first conceived definition of the meter length, an attempt to define a length in terms of a time. This attempt was made in order to do away with the nationalism of units of measure, and to make an international system possible. Officially the meter became defined as 1/10,000,000 of longitudinal length from north pole to equator through Paris. Todays definition of the meter defines it in terms of the second once more.

The second is also an official SI unit, one of the seven base SI units of measure, and is integral to the metric system and to modern science. Interestingly, the second has its basis in the sexigesimal system and a rather arbitrary division of the day, quite contrary to how the metric system operates. Perhaps a more scientifically-sound unit of time measurement will some day be derived.

The definition of the second has changed and evolved quite a bit through the ages. Currently the official scientific defintion has to do with quantum mechanics and the radiation of the cesium atom. They did this in order to make the second a unit that is unchanging with time (as the length of the day is changing over the millenia and so too would the second by extension). The first official scientific definition, however, was 1/86,400 of a mean solar day... even before they knew the length of the mean solar day. There had been other definitions in between adopted by the scientific community.

Good question. I don't know (though I doubt there was "a first"). It must be related to the fact that there are 60 seconds in a minute and 60 minutes in an hour, analogous to angles: 60 seconds in a minute and 60 minutes in a degree. Of course it breaks down from there: 24 hours in a day but 360 degrees in a circle. If you find out, let me know. There are no doubt historical reasons for the divisions by 60, but why the term "second"?