Ever wonder Why?

Manholes are round because if they were any other shape, their cover might easily fall through the hole. If manholes were square, rectangular oval or any other shape other than round, it would be possible to turn the cover so that its width would be less than one dimension  of the hole and this will enable the cover to fall through. This can't happen with round manhole since the width (or diameter) of the circle  measures the same in all direction.

Of course any shape can be used if the cover is larger than the opening of the manhole. The round manhole just permits the small cover.

------we have leap years?

We say there are 365 days in the year and by this we mean that it take the earth 365 days to make its annual trip around the sun. Actually, it takes the earth  365 1/2 days to make this trip. This means that every year we gain one-fourth of a day and every four years we gain one full day. If we did nothing about this, our calendar would move backward one full day every four years relative to our seasons.

To keep this from happening, we capture the extra day every four years and put it into our smallest month, February.