Repetitive surveillance by polar-orbiting meteorological satellites can monitor the distribution, variability, and behaviour of sea ice in both Arctic and Antarctic regions. This article reviews some of the applications of Nimbus satellite data to the polar regions. For a good review of applications of NOAA (formerly ESSA) satellite data to the polar regions, see Swithinbank (1969, 1970, 1971).

Most of the highly populated regions of the world are in the middle latitudes of the northern hemisphere. The shortest routes between some of them (and they happen to be the most advanced technologically) lie across the Arctic regions. The possibility of using these routes on a commercial scale has become real only comparatively recently, as technology has found ways of dealing with the distances and the natural obstacles. The transport systems with significant international applications are by sea and air. Land transport, whether by road or rail, crosses few frontiers (north of the Arctic Circle, only into and within Scandinavia) and raises no problems of special interest.

The Franklin Search continues through this instalment of our list, the main search culminating in the discovery by M'Clintock's expedition of the record that told of the Franklin expedition's success in finding a North-west Passage, of Franklin's death, and of the abandonment of his ships. Later, C. F. Hall and Frederick Schwatka discovered more bones and relics, which, however, added little to the bare outline of that tragic drama.