#23 in the series. Grosset and Dunlap. Copyright 1964. Rear cover lists to Repelatron Skyway (1963), and therefore the print run is estimated at about 1964. Not a first edition; likely a second or third printing made in 1964, the same year as the first printing. Very nice, sturdy picture cover. Black/white space lab endpapers. Front free endpaper has a hole in it, as if someone erased too hard. In ink, there's a prior owner name. No other writing/markings, no tracking, some corner bumping. In this one, Tom invents a “sea bloodhound” in the form of an underwater machine that tracks the metallic and chemical traces left by an object traveling through water. This machine has “driftometers” that automatically calculate particle dispersal due to measured oceanic drifts that have altered the course of the ship or whatever is being tracked, and in this way corrects the path to follow. TS23D