AT the Friday evening discourse at the Royal Institution on January 20, Dr. F. Fraser Darling described the island of North Rona. It is Britain's loneliest island; it lies forty-five miles north-west of Cape Wrath and north-east of the Butt of Lewis and is less than half a square mile in area. The island consists of Hebridean gneiss, but being free of peat and covered with a thin layer of soil, it differs radically from Lewis in its vegetative covering, which is of grass, quite free from heather. St. Ronan is reputed to be the first human inhabitant of Rona in the eighth century A.D. He built a cell almost underground, and much of the original building is still present. A chapel was built somewhat later contiguous with the cell and at its western end. Dr. and Mrs. Fraser Darling have excavated the accumulated stone and earth from the chapel and cell, disclosing the altar supports of masonry in the chapel, the rammed clay floor, the doorway into the cell, the original stone paving of the earlier building and the altar of masonry in the cell. Many quern stones and two fragments of stone vessels have been found. The wild life of Rona is of exceptional interest. There is an immense summer population of guillemots, razorbills, puffins, fulmar petrels, kittiwakes and great black-backed gulls. The storm petrel is also numerous, and Rona is one of the three British stations where Leach's fork-tailed petrel breeds. Rona is the headquarters of the Atlantic grey seal in Scottish waters, and a study of the social behaviour of this animal in the months it is ashore for breeding was the main purpose of Dr. Fraser Darling's expedition. Although this seal cannot dispense with the land for reproduction, this annual association with the land is a time of great danger. The social system is finely adapted to reducing the danger, and so are the animal's metabolic processes. The maiden cows and immature stock, for example, do not come ashore on the main mass of the island at the breeding season, but remain on skerries constantly ringed with surf. The calves feed from their mothers intensively for three weeks and are then weaned and left to find the sea for themselves. As the gestation period is 11-months, mating takes place while the mothers are ashore with their calves.