finder, in law. Ordinarily the finder of lost property is entitled to retain it against anyone except the owner. It is larceny, however, for the finder to keep the property if he knows or can easily determine who owns it. In some places the finder must deliver the lost object to the police; if it is unclaimed within a prescribed period it becomes his property. Lost objects that are embedded in the soil, e.g., a deeply buried ring, belong to the landowner even if another finds them. On the other hand, objects found in a privately owned place to which the public has the right of access, e.g., a hotel, belong to the finder and not to the owner of the realty. The purchaser of an article that, without his knowledge, has something of value concealed in it, e.g., money in a desk, is legally the finder, not the owner, of the valuable. See treasure-trove.

direction finder, electronic device used to determine the position of a ship or aircraft. In a simple direction finder a radio receiver is equipped with a revolving directional antenna. The antenna receives the strongest radio signal when it is pointing directly at a transmitter. By determining the direction of two land-based transmitters, a navigator may plot his position by triangulation. Direction finders have been replaced in many applications with more accurate systems, such as radar and satellite navigation systems (see satellite, artificial).

automatic direction finder: see radio range.

Instrument used to measure the distance from the instrument to a selected point or object. The optical range finder, used chiefly in cameras, consists of an arrangement of lenses and prisms set at each end of a tube. The object's range is determined by measuring the angles formed by a line of sight at each end of the tube; the smaller the angles, the greater the distance, and vice versa. Since the mid-1940s, radar has replaced optical range finders for most military targeting, and the laser range finder, developed in 1965, has largely replaced optical range finders for surveying and radar in certain military applications.

Learn more about range finder with a free trial on Britannica.com.