It's not very clear, but since he's talking about "the ancients", I think he's referring to the lodestone. Prior to the invention of the modern needle-type compass, the lodestone was a lump of magnetised rock which indicated the direction of Magnetic North. The ancients would also have used the stars and a sextant (or more likely a quadrant or an astrolabe at that time).
The SR-71 has an astro-tracker. A photo-electric cell can be locked onto a star and can even continue to track it in quite broad daylight. It's not particularly good at giving a position, but it is a very accurate source of heading - and therefore replaces the compass.
I think that that is what Gann was trying to say - but I agree that his prose is a bit purple in this particular passage. He must have been getting old by the time he wrote this. In general, he's one of the best of aviation writers.