Or, perhaps, "The Lost History" would be a better title. There is an awful lot of crucial information about the character of the Sandman hidden away in the two Sandman stories in the 1939 and 1940 New York World's Fair Comics. Indeed, until reading these stories in the DC Comics Rarities Archive, I have to say I didn't have a full understanding of who the Sandman was.
Right off the bat, we learn that the Sandman has an amazing amount of back story we have never learned about. This one panel begs the questions -- which other continent (we can presume one is North America)? What crimes is he suspected of?
Billions. Until DC later retconned Bruce Wayne into being a billionaire, the Sandman was the richest superhero in the DC Comics pantheon. And note here that he has invented a raygun for the government that he, as the Sandman, has never chosen to use. This is a man who uses a gas gun, not because it is the best weapon available to him, but because it is a weapon that leaves him with an element of risk. And, when even that doesn't leave him vulnerable enough, he will later go unarmed except for a 'wirepoon' gun.
This is Agent Henry of the Secret Service. He's apparently this Javert-like character who's been on the trail of the innocent Sandman for years, trying to arrest him. It's a shame this conflict is resolved in his very first published appearance.
Later retcons often show the Sandman wearing an ordinary gas mask, but this panel clearly shows, better than any drawing I'd seen before, what the Sandman's highly stylized gas mask is meant to look like. It's easy for those comfortable with the superhero genre to dismiss the Sandman as just a guy in a suit, but the Sandman was a man in a mask, suit optional. Here he runs around shirtless, having swum out to a yacht to confront the bad guys.
Another preconceived notion I had about the Sandman was that he routinely patrolled New York City, or a New York City-like fictional city, like Gotham City or Metropolis. But in 1940 New York World's Fair Comics, the Sandman is home, in a city that isn't in New York, and has to fly to New York to attend the fair. Where is he from, then? My money is on Boston now, being the next biggest East Coast city after NYC circa 1940.