Map and Survey

The thirteenth entry is a isolinha, a line drawn through every point that holds the same value, and its first three letters are a trap English sets for itself. Here they are Greek: isos means equal, and it opens a long and orderly family. An isobar joins places of equal pressure, an isotherm places of equal temperature, an isotope sits in the same square of the table — topos is place — and an isosceles triangle has legs of equal length. Nothing in that family says anything about being set apart. Yet English has a second « iso- », and it is by far the commoner one: « to isolate » came in from the Italian isolato, made into an island, and behind that stands the Latin insula. « Insulate » is the same Latin word taken by the direct road instead, so those two are one word arriving twice. « Isolation » and « isobar » therefore share four letters and not a single ancestor. A isolinha belongs to the Greek half; isolar, which turns up in the same technical prose, belongs to the other, and the resemblance is an accident.