The story begins with Superman waking from a dream where his Daily Pla...excuse me, WGBS coworkers apparently know he and Clark are one and the same. This leads to a rare occurrence from 1970s Superman comics...Superman acting like a rational adult:
Well, then there's some nonsense about a super-villain with hypnotic powers which really doesn't matter, except it leads to revelations about the true nature of Superman's dual identity. Superman is forced to use his own power of "super-hypnosis" (God bless the Silver Age) to protect the good citizens of Metropolis from the villain's powers...specifically, he commands them to "resist all hypnotic influences!"
Later, Supes begins to get a clue that something's up when Lana Lang catches him in the act of changing:
When Superman tells Lana that he's disguising himself as Clark Kent, Lana dismisses the notion, saying that Superman looks nothing like Clark.
Later, after the villain has been dispatched, Clark gets some sketches made of himself in both his identities...only to find that while the Superman sketch is dead-on...
Clark determines that it is his own power of super-hypnosis that is convincing everyone that Clark looks so much different from Superman...and that the pieces of glass from the Kryptonian rocket ship that brought him to earth that were used to create his glasses* enhance that effect:
His eyes are always apparently emitting some low level hypnotic power, but when passing through the Kryptonian glass, his subconscious desire to separate his Clark and Superman identities is made manifest. A comment is made about camera's reproducing the effect perfectly, which is why photos of Clark don't seem to reveal his true appearance to anyone.
So, when Superman commanded everyone to resist hypnotic suggestions, he unwittingly undid his own hypnotic hoodoo, which is why Lana didn't see Superman as Clark, even when wearing Clark's get-up.
The upshot is that Superman used super-hypnosis to make himself look different as Clark Kent, the idea was suggested by a reader of the comic (a then-prolific letterhack), and after this issue was published, it was ignored.