One of television's most intellectually stimulating series of specials is probing and prodding again. Speaking Without Words, the third in the ''Smithsonian World'' series (Wednesday, March 14, 8-9 p.m., check local listings for repeats), investigates the unlikely ways that human beings communicate.
The show's real strength is that it subtly links seemingly unconnected material so that there is a flow of provocative information somehow connected to the great Smithsonian Institution.
The ''Smithsonian World'' series, produced by Martin Carr, written by Michael Winship, and charmingly hosted by David McCullough (who has become as genial and authoritative as the ubiquitous Alistair Cooke), is now one of the most popular fixtures on PBS. In ''Speaking Without Words,'' Mr. McCullough guides viewers on a tour of Smithsonian research installations involved in experimenting with gorilla sign language and forensic anthropology. There is a fascinating look at the portraiture of Civil War battle artists - who communicated a totally different story from the reality of the battlefield; a study of fantastic roadside buildings built in the '20s and '30s which communicate their use to travelers (such as an ice cream shop in the shape of an ice cream cone); and a demonstration of the Foucault Pendulum of the National Museum of American History, which reveals the language of mathematics. But perhaps the most elegant segment is a lesson in the language of abstract art by Abram Lerner, founding director of the Hirshhorn Museum. It is an earnest explanation of the development of abstract art and, if the vocabulary of abstract art still remains a bit obscure for non-artists, well, at least Mr. Lerner tries.
''Smithsonian World'' is co-produced by WETA, Washington, and the Smithsonian Institution, with a grant from the James S. McDonnell Foundation. The series is, in effect, the most delightfully unobtrusive museum tour on record, filled with constant little shocks of recognition as the bits and pieces of information are artfully pieced together to form a captivating hour of education-cum-entertainment.