A title used between 1970 and 1983 by Boskone to designate a scientists or engineer brought to the convention to talk about his specialty. This was something of a quasi-GoH position as the person involved was frequently from outside the sf community. Modern lists unanimously treat the Science Speaker as a GoH. The last person designated a Science Speaker was in 1983 at Boskone 20. Subsequently, the position was replaced by a special guest who was a GoH selected from outside the fields of writing (the GoH) and art (the Official Artist). Some Special Guests were scientists.
Note that this is distinct from Boskone's more recent Hal Clement Science Speaker position which is explicitly not a GoH.