The formula is used to measure the speed of ocean waves, like tsunamis, that have very long wavelengths relative to the depth of the water. Tsunamis can have wavelengths greater than 700 kilometers (the average ocean depth is 3-4 kilometers). The formula estimates the tsunami's speed while it is in deeper waters (as it approaches shallower coastal waters, the tsunami slows down, its wavelength shortens, and its height increases).
Head lice and their eggs (nits) soon perish if separated from their human host. Adult head lice can live only a day or so off the human head without blood for feeding. Nymphs (young head lice) can live only for several hours without feeding on a human.
Nits are found firmly attached to the hair shaft about 1/4 inch from the scalp. They are oval and usually light colored or white, and take about a week to hatch into a baby louse called a nymph, then take about seven days to mature. Adult lice can live up to 30 days on a person's head, if the lice falls off a person, it dies within two days. The best defense, is a strong offense when dealing with these pests - the sooner the better. Search for head lice when hair is wet.