Naturally, there exist three kinds of optical beams: parallel, divergent, and convergent (see Fig. 1.1.1). If a beam, either divergent or convergent, has a single point of intersection of all optical rays it is called a homocentric beam (Fig. 1.1.1b,c). An example of a non-homocentric beam is shown in Fig. 1.1.1 d.

The sands of thy short life are spent this hour, / And no hand in the universe can turn / Thy hourglass, if these gummed leaves be burnt / Ere thou canst mount up these immortal steps.

If Basiandong is added to the list, it will be the third potential world heritage site in the county, after the Peinan Archeological Site in Beinan Township (卑南) — the largest-known ancient stone coffin burial ground in the Pacific Rim area — and Orchid Island (蘭嶼, also known as Lanyu).

I wouldn't recommend doing surgery on yourself, unless it is a last resort.